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A NEW FILM
879 tissue. In other words, fractionation of isotopes is a proven fact in Nature. Lasnitzki and Brewer carried out an analysis of potassium in human cancer, and found that the isotopic tumours showed, if compared mineral of that with potassium, a slight but definite increase, thus indicating a corresponding decrease in the percentage of the heavy isotope "K. In an analysis of the potassium content in eleven cases of human cancer, the average percentage of 4’K was 6-5 (normal 6-9), the average isotopic ratio 39K/uK being 14.3 (normal 13-5). Since a deviation of this kind could not be observed with potassium in any of the normal tissues, it appeared that the isotopic constitution of potassium in normal tissues and tumours was appreciably different. In addition, it has been found that the potassium content of muscle from tumour-bearing animals, compared with the potassium in muscle from normal animals, showed a deviation similar to that observed with potassium in tumours,Io a finding of possible significance.
ratio 39K/uK of potassium in
In other words, fractionation of the isotopes of potassium by the renal tubules or cell membranes is a physiological possibility, and in cases of cancer it seems that there is a selective affinity for the lighter isotopes, including 4°K. The body is therefore carrying out a process akin to the electromagnetic separation of isotopes as carried out in the laboratory, and there is no reason to suppose that 40K as well as 39K would not be fractionated in the same way. There are therefore two separate factors for consideration; the first, that the intracellular content of potassium can be permanently in excess of body requirements, and that this would carry with it an increase in the minute intracellular radioactive content; the second, that this minute intracellular radioactive content may be further stepped up by a physiological fractionation of 40K.
might expect that tissues containing a large amount of potassium would be more liable to undergo malignant change. This is not necessarily true, since cancer-prone cells are those that undergo frequent mitosis, as for example the cells of the respiratory, alimentary, and endocrine systems. Mitosis is rare in muscle tissue, and so are neoplasms. It is true, however, that individuals on a high-potassium diet appear to be more liable to develop cancer. This association is firmly supported by circumstantial evidence. The incidence of tumours in animals is greater when they are fed on a liberal diet compared with those fed on an adequate but low-calorie diet, and it is also clear that there is a relationship between national income and diet, and national income and cancer. The higher the annual budget per head of population, the greater the incidence of diagnosed cancer, and this seems to be associated with the fact that the higher the income One
of the country the greater the amount of food consumed.ll Further, the consumption of protein and fat increases with the income of the country, and it is these foods that are high in
potassium content. The biological effects of high-intensity radiation are well known, but little or nothing has yet been learnt about the effects of low-intensity radiation on the human body. This is partly accounted for by the fact that most experimental animals are unsuitable owing to their short span of life ; in other words, these animals would die in the natural course of events before any effects of this lowintensity radiation became apparent. This extremely minute radiation is undoubtedly increased by the storage of
large
amount
amounts of potassium-e.g., many times the required to carry out all normal physiological
functions. How much
more
could this minute radiation
8. Rankama, K. Isotope Geology; p. 147. London, 1954. 9. Lasnitzki, A., Brewer, A. K. Cancer Res. 1941, 1, 776. 10. Lasnitzki, A., Brewer, A. K. ibid. 1942, 2, 494. 11. Data compiled from Food Balance Sheets (Food and Agriculture Organisation, Rome, 1955) and from Statistics of National Income and Expenditure (Statistical Office, United Nations, New York, 1955).
be increased as the result of the selective affinity of the renal tubules or cell membranes for the lighter isotopes 39K and the radioactive 4OK? And how significant could this be when it is realised that this radiation is both intracellular and intranuclear-in other words, placed at the fountain head of mitosis. It is not suggested that potassium is a causative factor in all cancers; indeed, the number of known carcinogens increases daily, each one more powerful than its predecessor. What I put forward for expert thought, however, is a hypothesis that potassium could be an initiating factor in the onset of an ordinary non-industrial type of cancer.
London, W.1.
DESMOND K. MULVANY. A NEW FILM
SIR,-May I make a brief comment on your very fair review of April 2 (p. 777) of the film They Breathe Again? The film is intended primarily for nurses, as well as for medical men who may never work in a respiratory unit, but may find useful a clear statement of the whys and wherefors in dealing with the types of poliomyelitis most dangerous to life. For this reason the question of biochemical control and the regulation of pulmonary ventilation were deliberately omitted, and these two subjects would seem to merit the production of a separate film. The Drager meter was used because of the larger size and clarity of the dial. I should add that the film can be borrowed from the hospital free of charge. Rush Green Hospital, Romford, E.
JAMES.
Essex.
PLACENTA PRÆVIA
SIR,-Certain points that arise from Professor reply (April 2) need further discussion.
Macafee’s
(1) It is not merely the " occasional case " of antepartum haemorrhage in which there is doubt about the cause of bleeding. In practice the problem is arising continually. Major placenta prxvia usually causes no diagnostic problem but rather the lesser ones in which bleeding can still be dangerous. Displacement of the presenting part as a sign of placenta prxvia is used alike in clinical and radiological examination; yet the difficulty of relying on clinical examination alone in many cases is shown by the fact that even when there are both antepartum haemorrhage and a high head, there will be found just as many cases without as with placenta prxvia. For instance, in our series only 13 out of 50 cases of placenta praevia showed significant displacement of the presenting part along with bleeding; yet out of 84 other patients who bled and subsequently were proved not to have placenta praevia no less than 25 were found to have a high head. That is the diagnostic problem which we feel can best be solved in selected cases by placentography, avoiding dangerous on the one hand and overanxious conservatism the other. (2) Professor Macafee has stressed the placenta praevia that has already begun to bleed. Surely it is even better to teach our students and still more so our future consultants (especially in these islands where conditions are favourable) to watch for the signs of placenta praevia before bleeding begins. Selective placentography can play an important part here too. If there is doubt about this Professor Macafee himself has surely dispelled it in his account of discovering by accident a number of cases (six, I think) of major placenta praevia at caesarean section for other reasons. This too stresses the importance of noting the difference between a high or elevated head not approaching the brim, and merely the unengaged one that does. The advantages that soft-tissue placentography can offer to the discerning outpatient clinician in such cases seem too obvious to mention.
complacency
on
ratio 39K/uK of potassium in
In other words, fractionation of the isotopes of potassium by the renal tubules or cell membranes is a physiological possibility, and in cases of cancer it seems that there is a selective affinity for the lighter isotopes, including 4°K. The body is therefore carrying out a process akin to the electromagnetic separation of isotopes as carried out in the laboratory, and there is no reason to suppose that 40K as well as 39K would not be fractionated in the same way. There are therefore two separate factors for consideration; the first, that the intracellular content of potassium can be permanently in excess of body requirements, and that this would carry with it an increase in the minute intracellular radioactive content; the second, that this minute intracellular radioactive content may be further stepped up by a physiological fractionation of 40K.
might expect that tissues containing a large amount of potassium would be more liable to undergo malignant change. This is not necessarily true, since cancer-prone cells are those that undergo frequent mitosis, as for example the cells of the respiratory, alimentary, and endocrine systems. Mitosis is rare in muscle tissue, and so are neoplasms. It is true, however, that individuals on a high-potassium diet appear to be more liable to develop cancer. This association is firmly supported by circumstantial evidence. The incidence of tumours in animals is greater when they are fed on a liberal diet compared with those fed on an adequate but low-calorie diet, and it is also clear that there is a relationship between national income and diet, and national income and cancer. The higher the annual budget per head of population, the greater the incidence of diagnosed cancer, and this seems to be associated with the fact that the higher the income One
of the country the greater the amount of food consumed.ll Further, the consumption of protein and fat increases with the income of the country, and it is these foods that are high in
potassium content. The biological effects of high-intensity radiation are well known, but little or nothing has yet been learnt about the effects of low-intensity radiation on the human body. This is partly accounted for by the fact that most experimental animals are unsuitable owing to their short span of life ; in other words, these animals would die in the natural course of events before any effects of this lowintensity radiation became apparent. This extremely minute radiation is undoubtedly increased by the storage of
large
amount
amounts of potassium-e.g., many times the required to carry out all normal physiological
functions. How much
more
could this minute radiation
8. Rankama, K. Isotope Geology; p. 147. London, 1954. 9. Lasnitzki, A., Brewer, A. K. Cancer Res. 1941, 1, 776. 10. Lasnitzki, A., Brewer, A. K. ibid. 1942, 2, 494. 11. Data compiled from Food Balance Sheets (Food and Agriculture Organisation, Rome, 1955) and from Statistics of National Income and Expenditure (Statistical Office, United Nations, New York, 1955).
be increased as the result of the selective affinity of the renal tubules or cell membranes for the lighter isotopes 39K and the radioactive 4OK? And how significant could this be when it is realised that this radiation is both intracellular and intranuclear-in other words, placed at the fountain head of mitosis. It is not suggested that potassium is a causative factor in all cancers; indeed, the number of known carcinogens increases daily, each one more powerful than its predecessor. What I put forward for expert thought, however, is a hypothesis that potassium could be an initiating factor in the onset of an ordinary non-industrial type of cancer.
London, W.1.
DESMOND K. MULVANY. A NEW FILM
SIR,-May I make a brief comment on your very fair review of April 2 (p. 777) of the film They Breathe Again? The film is intended primarily for nurses, as well as for medical men who may never work in a respiratory unit, but may find useful a clear statement of the whys and wherefors in dealing with the types of poliomyelitis most dangerous to life. For this reason the question of biochemical control and the regulation of pulmonary ventilation were deliberately omitted, and these two subjects would seem to merit the production of a separate film. The Drager meter was used because of the larger size and clarity of the dial. I should add that the film can be borrowed from the hospital free of charge. Rush Green Hospital, Romford, E.
JAMES.
Essex.
PLACENTA PRÆVIA
SIR,-Certain points that arise from Professor reply (April 2) need further discussion.
Macafee’s
(1) It is not merely the " occasional case " of antepartum haemorrhage in which there is doubt about the cause of bleeding. In practice the problem is arising continually. Major placenta prxvia usually causes no diagnostic problem but rather the lesser ones in which bleeding can still be dangerous. Displacement of the presenting part as a sign of placenta prxvia is used alike in clinical and radiological examination; yet the difficulty of relying on clinical examination alone in many cases is shown by the fact that even when there are both antepartum haemorrhage and a high head, there will be found just as many cases without as with placenta prxvia. For instance, in our series only 13 out of 50 cases of placenta praevia showed significant displacement of the presenting part along with bleeding; yet out of 84 other patients who bled and subsequently were proved not to have placenta praevia no less than 25 were found to have a high head. That is the diagnostic problem which we feel can best be solved in selected cases by placentography, avoiding dangerous on the one hand and overanxious conservatism the other. (2) Professor Macafee has stressed the placenta praevia that has already begun to bleed. Surely it is even better to teach our students and still more so our future consultants (especially in these islands where conditions are favourable) to watch for the signs of placenta praevia before bleeding begins. Selective placentography can play an important part here too. If there is doubt about this Professor Macafee himself has surely dispelled it in his account of discovering by accident a number of cases (six, I think) of major placenta praevia at caesarean section for other reasons. This too stresses the importance of noting the difference between a high or elevated head not approaching the brim, and merely the unengaged one that does. The advantages that soft-tissue placentography can offer to the discerning outpatient clinician in such cases seem too obvious to mention.
complacency
on