930 LYMPHATIC DRAINAGE OF THE BRAIN
SIR,-In contrast to the title of your editorial,’ Cerebrospinal Fluid: the Lymph of the Brain, modern lymphology defines lymph as a fluid inside lymph vessels and nodes. A sharp distinction is made between lymph and tissue fluid: the latter leaves blood capillaries and cells via "pre-lymphatic pathways"2 to the lymph capillaries. I see no benefit in calling cerebrospinal fluid (c.s.F.) the lymph of the brain, as has already been done in 1894.3 You describe the choroid plexus as the only route of reabsorption for protein molecules from C.S.F. and do not mention reabsorption into lymph vessels in the nasal cavity, the orbit, the’jugular foramen, &c. Furthermore, various corpuscular tracers-indian ink and ’Thorotrast’ particles,4 leucocytess-injected into the brain travel via the prelymphatic Virchow-Robin spaces of the cerebral bloodvessels, through the subarachnoid space, into the adventitial tissues of the extracranial segment of the same blood-vessels; here, they become reabsorbed by the vasa lymphatica vasorum and can be demonstrated in cervical lymph-nodes. After a cerebral haemorrhage, blood pigments, following processes leading to the destruction of brain-tissue cerebral lipids, travel along the same "prelymphatic/lymphatic drainage pathway".6 The functional significance of lymphatic drainage of the brain’ was demonstrated by studying experimental cervical lymphatic blockage. After this operation lymphostatic encephalopathy arises, with various functional and morphological changes.8 Protein molecules, injected into the subarachnoid space, penetrate the brain9; on the other hand, protein molecules, under normal circumstances, do not pass from lymphatics into the parenchyma of organs. Taking these facts into consideration, C.S.F. could be called tissue fluid of the brain-but not lymph. Lymphological Research Laboratory, Schaper and Brümmer, Salzgitter-Ringelheim, Federal Republic of Germany.
M. FÖLDI
COST OF BREAST-FEEDING
SIR,-As Dr Buss rightly points out (Oct. 18, p. 766) breastmilk is the best milk for a baby. He has attempted to assess the comparative cost of breast-feeding and comes up with figures of 11-14p per day (mean 12.5p.). For bottle-feeding with proprietary brands the figures are 1G-17. 5p per day (mean 13-75), and it is only if National Dried Milk (N.D.M.) is used that the cost of artificial feeding becomes substantially less, because there is a considerable subsidy not available to mothers who wish to do the best for their babies and breast-feed them. Omitting the now outmoded high-solute milks, of which N.D.M. is an example, and comparing on cost terms only breast-milk and the more modern and widely recommended low-solute milks’ (at present only available in expensive proprietary forms), then I believe that Dr Buss’s calculations favour human milk in financial terms of not less than one penny per day. Leaving aside this trivial cost difference, the benefits of successful breast-feeding are incalculable in terms of mother-child bonding, anti-infective properties, and as a shield against metabolic disorders (hypocalcaemia and hypernatrtmia), obesity, and possibly the risk of cot death. Maternal health may 1. 2.
Lancet, Sept. 6, 1975, p. 444. Casley-Smith, J. R. in The Inflammatory Process (edited by B. W. Zweifach, L. Grant, and R. T. McCluskey). New York, 1973. 3. Tuke, J. B. Edinb. med. J. 1894, 39, 673. 4. Kozma, M., Zoltan, O. T., Csillik, B. Acta anat 1972, 81, 409. 5. Oehmichen, M., Gencic, M. Acta neuropath. 1975, 6, suppl. p. 285. 6. Csanda, E. Folia Angiol. 1974, 22, 29. 7. Földi, M., Csillik, B., Zoltan, O. T. Experientia, 1968, 24, 1283. 8. Földi, M. Diseases of Lymphatics and Lymph Circulation. Springfield, Illinois, 1969. 9. Klatzo, I., Wisniewski, H., Smith, D. E. in Progress in Brain Research, (edited by E. D. P. de Robertis and R. Carrea). Amsterdam, 1965. 1. Present Day Practice in Infant Feeding. H. M. Stationery Office, 1974.
also be improved by breast-feeding, since milk production uses up food stores laid down in pregnancy for this very purpose, thus discouraging the development of maternal obesity. Because of this one wonders whether all the extra food said to be consumed by the lactating mother is always strictly necessary or desirable. The unique advantages of breast-feeding are such that most women who correctly choose to breast-feed their babies will do so for better reasons than to save a penny or so a day. The Children’s
Hospital,
Cheltenham,
R. D. G. CREERY
Gloucestershire.
GASTRIC EMPTYING IN LABOUR
SIR,-In their rejoinder to a letter’ on gastric emptying in labour Dr Nimmo and his colleagues ask us to confirm the complete avoidance of drug therapy or analgesia in our studies.23 We can only repeat that no patient received any drug during our study. This cannot be considered unusual by anyone knowledgeable and experienced in obstetrics-especially in the developing countries at the time this work was done. It is clear to us that the impaired gastric emptying in labour which we have observed can only be related to factors associated with labour itself and not to extraneous factors introduced by various forms of clinical intervention-including the
use
of drugs.
We see no reason to change our hypothesis of a stress-induced inhibition of gastric tone and motility to explain these results. The suggestion of some hypothetical and unspecified form of stress, induced only in our test (labouring) group by the use of a nasogastric tube and a 750 ml test meal, appears to us to be improbable. Some of these subjects, acting as their own control, had previously experienced these procedures and all the patients admitted to being unconcerned by the presence of the tube at the actual time of testing, one hour after intubation. According to our estimates, which take into account the difference in the volume of the meals, the degree of inhibition we observed is similar to that reported by Nimmo et al. As we stated clearly in our paper,2there was no exponential relationship between volume and time in the labouring group. We further pointed out that in each patient there was an initial rapid emptying over the first ten minutes during which the volume fell by almost a third but that the residual volume required a far greater time to empty. It is clear from this description that the time taken for the gastric volume to fall by half is longer at volumes below 200-300 ml. The estimated times for the volumes to fall from 200 ml to 100 ml (i.e., the "half-life" as defined by Nimmo et al.) are comparable to, or in excess of, the values cited by these authors. We do not dispute the well-established effects of narcotic analgesics which lead to an inhibition of gastric emptying.4 However, we question the conclusion of the study of paracetamol absorption kinetics in labour.5 The authors are surely bound by their own argument in which they consider two possible explanations of the results: (1) a physiological response caused by stress in the later stages of labour, and (2) a pharmacologically induced effect. They reject the former hypothesis, not because of any positive evidence, but because of a lack of certain specific information in our previous paperwhich now we have supplied. This information on the proximity of delivery’ and the lack of drug therapy in our studies supports the first of these two
hypotheses.
With
regard
to
the
paracetamol absorption method,
there
1. Davison, 2. Davison,
J. S. Lancet, Aug. 2, 1975, p. 227. J. S., Davison, M. C., Hay, D. M.J. Obstet. Gynœc Br Commonw. 1970, 77, 37. 3. Davison, J. S., Davison, M. C., Hay, D. M. West Indian medJ 1970, 19, 259.
4.
Jaffe, J. H.
in
The
Pharmacological
Basis of Therapeutics
(edited by I S
Goodman and A. Gilman); p. 245. New York, 1970. 5. Nimmo, W. S., Wilson, J., Prescott, L. F. Lancet, 1975, i, 890
931 intention of questioning the underlying principle or the validity of the technique. We merely wish to place on record that we disapprove of the practice of publishing results before was no
publishing the validation
of the’method used
to
obtain them.
University Department
of Physiology,
J. S. DAVISON
Dundee DD1 4HN.
Faculty of Medicine, University of Calgary, Alberta, Canada.
D. M. HAY
DOES NITROUS OXIDE HARM THE DENTIST ?
SIR,-Ever since Bruce and his co-workerssuggested link between the pollution of operating-theatres with anxsthetic gases and causes of death in anxsthetists there has been concern over the problem. Halothane has been the main object of this concern but nitrous oxide is not innocuous. Lassen and his colleagueshave reported severe bone-marrow depression after prolonged nitrousoxide anaesthesia, and the gas has also been shown to be teratogenic under experimental conditions. 3-5 This latter effect may be associated with an increased spontaneousabortion rate in female doctors and nurses.6 Pollution of the dental surgery with anxsthetic gases is also common. Levels of halothane have been found to be high,’ and a were highest in the region of the dental surgeon’s face." there is an in the use of e nitrous oxide Today upsurge as a means of sedation in dentistry. It appears safe for the patient who inhales it for a relatively short time. But is it safe for the dentist and his staff who may inhale it over a long period ?? As part of our investigation of the problem we have exposed albino rats to a 1 % level of nitrous oxide for six hours per day, five days per week. This pollution level is equivalent to that reported in a dental surgery by Millard and Corbett,9 and the exposure-time fairly closely mimics a typical dentist’s day when using nitrous-oxide/oxygen sedation (relative analgesia). After nine weeks’ exposure no difference was found between the hsmatological appearances of the peripheral blood in experimental and control animals. However, after five weeks’ exposure to nitrous oxide there was a marked increase in the numbers of mast cells, particularly in the bone-marrow where they averaged 10 per oil-immersion field. The exact role of the mast cells in this experimental situation is not yet clear, but their presence does suggest that the bone-marrow is under stress. 10 Further experiments are under way and full details will be published
a
PARTICLES ASSOCIATED WITH MICROVILLOUS BORDER OF INTESTINAL MUCOSA
SIR,-Electron-microscope observations often form part of studies on viral and other infections of the intestine, in both man and animals. Micrographs of the apical border of normal intestinal epithelial cells commonly depict a regular array of intact microvilli of equal length, while pathological change in an epithelial cell often features the loss of many microvilli, the remainder being of irregular distribution and length. An electron-microscope study of human jejunal biopsies by Dr Tomkins and others (July 5, p. 36) showed particles resembling oncornavirus, arenavirus, and mycoplasma. One of their micrographs (their fig. 3), in addition to demonstrating mycoplasma-like particles, showed particles with a circular profile aligned in the spaces between microvilli. We have observed similar particles in intestinal samples from pigs. They resemble viral particles in size and appearance and, in addition to their intrinsic interest, their differentiation from known infectious agents needs to be taken into consideration. The
specimens
were
fixed in
glutaraldehyde, post-fixed
tetroxide, and embedded in ’Araldite’; ultrathin
in osmium
stained with uranyl acetate and lead citrate and examined in a Philips EM 300 electron microscope. In each specimen the particles were seen associated with a minority of cells. Fig. 1 shows particles associated with an epithelial cell with rather dense cytoplasm. The microvilli appear to be pinched and beaded in such a way that the particles may be derived from the beads. Higher magnification (fig, 2) shows that the particles have a unit membrane and diameter of 60-75 nm. The particles were seen in the duodenal, Iejunal, and ileal portions of the small intestine of a 9-day-old gnotobiotic piglet and m the jejunal and ileal portions of the intestine of 3 siblings similarlv reared but experimentally infected with neonatal-calf-diarrhoea reovirus-like agent (rotavirus). The particles were not seen in a further umnfected sibling or in 3 further rotavirus-tnfected siblings. The particles were also seen in a mucosal sample obtained from a 1-week-old gnotobiotic pig and maintained for 30 minutes in organ culture in the presence of Escherichia. coli. They were not seen in a sample from the same pig maintained without E. coli. Neither were they seen in samples, maintained in organ culture with or without E. coli, from 3 other pigs. A search made on a further uninoculated gnotobiotic pig, on 2 gnotobiotic pigs inoculated with transmissible gastroenteritis virus, and on 4 pigs inoculated with a rotavirus and an enterovirus did not demonstrate the particles. sections were
These results show that the particles can be found in gnotobiotic pigs, whether or not these pigs have been experimentally infected. They could be differentiated from the virus particles
elsewhere. Dental Research Unit, South African Medical Research Council and University of the Witwatersrand, Jan Smuts Avenue,
Johannesburg 2001, South Africa.
P. CLEATON-JONES J. C. AUSTIN D. BANKS E. VIEIRA.
National Research Institute for
Occupational Diseases, South African Medical Research
Council, Civic Centre,
Johannesburg 2001, South Africa.
E. KAGAN.
Bruce, D. L., Eide, K. A., Linde, H. W., Eckinhoff, J. E. Anesthesiology, 1968, 29, 565. 2. Lassen, H. C. A., Henrickson, E., Neukirch, F., Kirstensen, H. S. Lancet, 1956, i, 527. 3. Rector, G. H. M., Eastwood, D. N. Anesthesiology, 1964, 25, 109. 4 Smith, B. E., Gaub, M. L., Moya, F. Anesth. Analg. 1965, 44, 726. 5. Fink, B. R., Shepard, T. H., Blandau, R. J. Nature, 1967, 214, 146. 6 Vaisman, A. I. Éksp. Khir. Anest. 1967, 3, 44. 7. Strunin, L., Strunin, J. M., Mallios, C. C. Br. med. J. 1973, iv, 459. 8. Mallios, C. C., Strunin, J. M., Strunin, L. Br. dent. J. 1974, 136, 1.
449.
Millard, R. I., Corbett, T. H. J. Oral Surg. 1974, 32, 593. 10. Selye, H. The Mast Cells; p. 403, Washington, 1965. 9.
Fig. 1-Apical surface of mucosal cell. Particles with a circular profile associated with microvilli having a beaded appearance.
are
SIR,-In contrast to the title of your editorial,’ Cerebrospinal Fluid: the Lymph of the Brain, modern lymphology defines lymph as a fluid inside lymph vessels and nodes. A sharp distinction is made between lymph and tissue fluid: the latter leaves blood capillaries and cells via "pre-lymphatic pathways"2 to the lymph capillaries. I see no benefit in calling cerebrospinal fluid (c.s.F.) the lymph of the brain, as has already been done in 1894.3 You describe the choroid plexus as the only route of reabsorption for protein molecules from C.S.F. and do not mention reabsorption into lymph vessels in the nasal cavity, the orbit, the’jugular foramen, &c. Furthermore, various corpuscular tracers-indian ink and ’Thorotrast’ particles,4 leucocytess-injected into the brain travel via the prelymphatic Virchow-Robin spaces of the cerebral bloodvessels, through the subarachnoid space, into the adventitial tissues of the extracranial segment of the same blood-vessels; here, they become reabsorbed by the vasa lymphatica vasorum and can be demonstrated in cervical lymph-nodes. After a cerebral haemorrhage, blood pigments, following processes leading to the destruction of brain-tissue cerebral lipids, travel along the same "prelymphatic/lymphatic drainage pathway".6 The functional significance of lymphatic drainage of the brain’ was demonstrated by studying experimental cervical lymphatic blockage. After this operation lymphostatic encephalopathy arises, with various functional and morphological changes.8 Protein molecules, injected into the subarachnoid space, penetrate the brain9; on the other hand, protein molecules, under normal circumstances, do not pass from lymphatics into the parenchyma of organs. Taking these facts into consideration, C.S.F. could be called tissue fluid of the brain-but not lymph. Lymphological Research Laboratory, Schaper and Brümmer, Salzgitter-Ringelheim, Federal Republic of Germany.
M. FÖLDI
COST OF BREAST-FEEDING
SIR,-As Dr Buss rightly points out (Oct. 18, p. 766) breastmilk is the best milk for a baby. He has attempted to assess the comparative cost of breast-feeding and comes up with figures of 11-14p per day (mean 12.5p.). For bottle-feeding with proprietary brands the figures are 1G-17. 5p per day (mean 13-75), and it is only if National Dried Milk (N.D.M.) is used that the cost of artificial feeding becomes substantially less, because there is a considerable subsidy not available to mothers who wish to do the best for their babies and breast-feed them. Omitting the now outmoded high-solute milks, of which N.D.M. is an example, and comparing on cost terms only breast-milk and the more modern and widely recommended low-solute milks’ (at present only available in expensive proprietary forms), then I believe that Dr Buss’s calculations favour human milk in financial terms of not less than one penny per day. Leaving aside this trivial cost difference, the benefits of successful breast-feeding are incalculable in terms of mother-child bonding, anti-infective properties, and as a shield against metabolic disorders (hypocalcaemia and hypernatrtmia), obesity, and possibly the risk of cot death. Maternal health may 1. 2.
Lancet, Sept. 6, 1975, p. 444. Casley-Smith, J. R. in The Inflammatory Process (edited by B. W. Zweifach, L. Grant, and R. T. McCluskey). New York, 1973. 3. Tuke, J. B. Edinb. med. J. 1894, 39, 673. 4. Kozma, M., Zoltan, O. T., Csillik, B. Acta anat 1972, 81, 409. 5. Oehmichen, M., Gencic, M. Acta neuropath. 1975, 6, suppl. p. 285. 6. Csanda, E. Folia Angiol. 1974, 22, 29. 7. Földi, M., Csillik, B., Zoltan, O. T. Experientia, 1968, 24, 1283. 8. Földi, M. Diseases of Lymphatics and Lymph Circulation. Springfield, Illinois, 1969. 9. Klatzo, I., Wisniewski, H., Smith, D. E. in Progress in Brain Research, (edited by E. D. P. de Robertis and R. Carrea). Amsterdam, 1965. 1. Present Day Practice in Infant Feeding. H. M. Stationery Office, 1974.
also be improved by breast-feeding, since milk production uses up food stores laid down in pregnancy for this very purpose, thus discouraging the development of maternal obesity. Because of this one wonders whether all the extra food said to be consumed by the lactating mother is always strictly necessary or desirable. The unique advantages of breast-feeding are such that most women who correctly choose to breast-feed their babies will do so for better reasons than to save a penny or so a day. The Children’s
Hospital,
Cheltenham,
R. D. G. CREERY
Gloucestershire.
GASTRIC EMPTYING IN LABOUR
SIR,-In their rejoinder to a letter’ on gastric emptying in labour Dr Nimmo and his colleagues ask us to confirm the complete avoidance of drug therapy or analgesia in our studies.23 We can only repeat that no patient received any drug during our study. This cannot be considered unusual by anyone knowledgeable and experienced in obstetrics-especially in the developing countries at the time this work was done. It is clear to us that the impaired gastric emptying in labour which we have observed can only be related to factors associated with labour itself and not to extraneous factors introduced by various forms of clinical intervention-including the
use
of drugs.
We see no reason to change our hypothesis of a stress-induced inhibition of gastric tone and motility to explain these results. The suggestion of some hypothetical and unspecified form of stress, induced only in our test (labouring) group by the use of a nasogastric tube and a 750 ml test meal, appears to us to be improbable. Some of these subjects, acting as their own control, had previously experienced these procedures and all the patients admitted to being unconcerned by the presence of the tube at the actual time of testing, one hour after intubation. According to our estimates, which take into account the difference in the volume of the meals, the degree of inhibition we observed is similar to that reported by Nimmo et al. As we stated clearly in our paper,2there was no exponential relationship between volume and time in the labouring group. We further pointed out that in each patient there was an initial rapid emptying over the first ten minutes during which the volume fell by almost a third but that the residual volume required a far greater time to empty. It is clear from this description that the time taken for the gastric volume to fall by half is longer at volumes below 200-300 ml. The estimated times for the volumes to fall from 200 ml to 100 ml (i.e., the "half-life" as defined by Nimmo et al.) are comparable to, or in excess of, the values cited by these authors. We do not dispute the well-established effects of narcotic analgesics which lead to an inhibition of gastric emptying.4 However, we question the conclusion of the study of paracetamol absorption kinetics in labour.5 The authors are surely bound by their own argument in which they consider two possible explanations of the results: (1) a physiological response caused by stress in the later stages of labour, and (2) a pharmacologically induced effect. They reject the former hypothesis, not because of any positive evidence, but because of a lack of certain specific information in our previous paperwhich now we have supplied. This information on the proximity of delivery’ and the lack of drug therapy in our studies supports the first of these two
hypotheses.
With
regard
to
the
paracetamol absorption method,
there
1. Davison, 2. Davison,
J. S. Lancet, Aug. 2, 1975, p. 227. J. S., Davison, M. C., Hay, D. M.J. Obstet. Gynœc Br Commonw. 1970, 77, 37. 3. Davison, J. S., Davison, M. C., Hay, D. M. West Indian medJ 1970, 19, 259.
4.
Jaffe, J. H.
in
The
Pharmacological
Basis of Therapeutics
(edited by I S
Goodman and A. Gilman); p. 245. New York, 1970. 5. Nimmo, W. S., Wilson, J., Prescott, L. F. Lancet, 1975, i, 890
931 intention of questioning the underlying principle or the validity of the technique. We merely wish to place on record that we disapprove of the practice of publishing results before was no
publishing the validation
of the’method used
to
obtain them.
University Department
of Physiology,
J. S. DAVISON
Dundee DD1 4HN.
Faculty of Medicine, University of Calgary, Alberta, Canada.
D. M. HAY
DOES NITROUS OXIDE HARM THE DENTIST ?
SIR,-Ever since Bruce and his co-workerssuggested link between the pollution of operating-theatres with anxsthetic gases and causes of death in anxsthetists there has been concern over the problem. Halothane has been the main object of this concern but nitrous oxide is not innocuous. Lassen and his colleagueshave reported severe bone-marrow depression after prolonged nitrousoxide anaesthesia, and the gas has also been shown to be teratogenic under experimental conditions. 3-5 This latter effect may be associated with an increased spontaneousabortion rate in female doctors and nurses.6 Pollution of the dental surgery with anxsthetic gases is also common. Levels of halothane have been found to be high,’ and a were highest in the region of the dental surgeon’s face." there is an in the use of e nitrous oxide Today upsurge as a means of sedation in dentistry. It appears safe for the patient who inhales it for a relatively short time. But is it safe for the dentist and his staff who may inhale it over a long period ?? As part of our investigation of the problem we have exposed albino rats to a 1 % level of nitrous oxide for six hours per day, five days per week. This pollution level is equivalent to that reported in a dental surgery by Millard and Corbett,9 and the exposure-time fairly closely mimics a typical dentist’s day when using nitrous-oxide/oxygen sedation (relative analgesia). After nine weeks’ exposure no difference was found between the hsmatological appearances of the peripheral blood in experimental and control animals. However, after five weeks’ exposure to nitrous oxide there was a marked increase in the numbers of mast cells, particularly in the bone-marrow where they averaged 10 per oil-immersion field. The exact role of the mast cells in this experimental situation is not yet clear, but their presence does suggest that the bone-marrow is under stress. 10 Further experiments are under way and full details will be published
a
PARTICLES ASSOCIATED WITH MICROVILLOUS BORDER OF INTESTINAL MUCOSA
SIR,-Electron-microscope observations often form part of studies on viral and other infections of the intestine, in both man and animals. Micrographs of the apical border of normal intestinal epithelial cells commonly depict a regular array of intact microvilli of equal length, while pathological change in an epithelial cell often features the loss of many microvilli, the remainder being of irregular distribution and length. An electron-microscope study of human jejunal biopsies by Dr Tomkins and others (July 5, p. 36) showed particles resembling oncornavirus, arenavirus, and mycoplasma. One of their micrographs (their fig. 3), in addition to demonstrating mycoplasma-like particles, showed particles with a circular profile aligned in the spaces between microvilli. We have observed similar particles in intestinal samples from pigs. They resemble viral particles in size and appearance and, in addition to their intrinsic interest, their differentiation from known infectious agents needs to be taken into consideration. The
specimens
were
fixed in
glutaraldehyde, post-fixed
tetroxide, and embedded in ’Araldite’; ultrathin
in osmium
stained with uranyl acetate and lead citrate and examined in a Philips EM 300 electron microscope. In each specimen the particles were seen associated with a minority of cells. Fig. 1 shows particles associated with an epithelial cell with rather dense cytoplasm. The microvilli appear to be pinched and beaded in such a way that the particles may be derived from the beads. Higher magnification (fig, 2) shows that the particles have a unit membrane and diameter of 60-75 nm. The particles were seen in the duodenal, Iejunal, and ileal portions of the small intestine of a 9-day-old gnotobiotic piglet and m the jejunal and ileal portions of the intestine of 3 siblings similarlv reared but experimentally infected with neonatal-calf-diarrhoea reovirus-like agent (rotavirus). The particles were not seen in a further umnfected sibling or in 3 further rotavirus-tnfected siblings. The particles were also seen in a mucosal sample obtained from a 1-week-old gnotobiotic pig and maintained for 30 minutes in organ culture in the presence of Escherichia. coli. They were not seen in a sample from the same pig maintained without E. coli. Neither were they seen in samples, maintained in organ culture with or without E. coli, from 3 other pigs. A search made on a further uninoculated gnotobiotic pig, on 2 gnotobiotic pigs inoculated with transmissible gastroenteritis virus, and on 4 pigs inoculated with a rotavirus and an enterovirus did not demonstrate the particles. sections were
These results show that the particles can be found in gnotobiotic pigs, whether or not these pigs have been experimentally infected. They could be differentiated from the virus particles
elsewhere. Dental Research Unit, South African Medical Research Council and University of the Witwatersrand, Jan Smuts Avenue,
Johannesburg 2001, South Africa.
P. CLEATON-JONES J. C. AUSTIN D. BANKS E. VIEIRA.
National Research Institute for
Occupational Diseases, South African Medical Research
Council, Civic Centre,
Johannesburg 2001, South Africa.
E. KAGAN.
Bruce, D. L., Eide, K. A., Linde, H. W., Eckinhoff, J. E. Anesthesiology, 1968, 29, 565. 2. Lassen, H. C. A., Henrickson, E., Neukirch, F., Kirstensen, H. S. Lancet, 1956, i, 527. 3. Rector, G. H. M., Eastwood, D. N. Anesthesiology, 1964, 25, 109. 4 Smith, B. E., Gaub, M. L., Moya, F. Anesth. Analg. 1965, 44, 726. 5. Fink, B. R., Shepard, T. H., Blandau, R. J. Nature, 1967, 214, 146. 6 Vaisman, A. I. Éksp. Khir. Anest. 1967, 3, 44. 7. Strunin, L., Strunin, J. M., Mallios, C. C. Br. med. J. 1973, iv, 459. 8. Mallios, C. C., Strunin, J. M., Strunin, L. Br. dent. J. 1974, 136, 1.
449.
Millard, R. I., Corbett, T. H. J. Oral Surg. 1974, 32, 593. 10. Selye, H. The Mast Cells; p. 403, Washington, 1965. 9.
Fig. 1-Apical surface of mucosal cell. Particles with a circular profile associated with microvilli having a beaded appearance.
are
