NA TURE 



[August 12, 1922 



Letters to the Editor. 



[The Editor docs not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended J or 

 this or any other part of Nature. No notice is 

 taken of anon vinous communications.'] 



The Cause of Rickets. 



The scientific interest of the work that has been 

 done and is reviewed in the leading article in Nature 

 of July 29, p. 137, is that it shows that ultra-violet 

 light, acting on the skin, produces by a photo- 

 chemical reaction a definite substance which circulates 

 in the blood. This substance is able to replace 

 vitamin-A in the food ; whether wholty or only 

 partially is not yet certain, although it should not be 

 difficult to decide the question. If the former, it 

 appears that light actually causes the formation of 

 the vitamin, as suggested by Prof. Harden, or at all 

 events some compound closely similar to it. Dr. 

 Rollier finds in his sunlight treatment of tuberculosis 

 that cod-liver oil is quite unnecessary ; but, of course, 

 his patients get vitamin-A in butter and so on. In 

 rickets, vitamin-A can apparently be reduced to a 

 very small amount if there is plenty of sunlight, but 

 it is uncertain whether the vitamin can completely 

 replace sunlight. 



Looking at the evidence as a whole, it seems to me 

 that the six or seven causes enumerated in Dr. 

 Findlay's article may really be reduced to two and 

 perhaps ultimately to one. These two are deficiency 

 of sunlight and of vitamin-A. Taking the remaining 

 suggested causes in the order mentioned, it is obvious 

 that bone cannot be made without its constituents 

 calcium and phosphate, and, as the article points out, 

 this is not a matter of great practical importance, 

 especially if a proper quantity of milk is included in 

 the diet. As to the avoiding of cereals in favour of 

 meat, it seems that the question here is really one of 

 the rate of growth. There is no doubt that the more 

 rapid the growth, the more vitamin-A is needed, 

 probably because it is stored to some extent in the 

 new tissues, especially if these consist of much fat. 

 Prof. Mellanby's experiments showed clearlv that the 

 addition of carbohydrate to the diet of his puppies 

 necessitated more vitamin because the growth was so 

 much more rapid than on meat diet alone. It is of 

 interest that Dr. Rollier's experience with tuberculous 

 cases is at variance with Dr. Findlay's with rickets. 

 Rollier finds that much meat is injurious, and that 

 oatmeal is one of the best foods. At the same time, 

 he deprecates over-feeding. 



The next cause, rapid growth, has been dealt with 

 above. 



I am inclined to think that the factors included in 

 bodity confinement and lack of exercise actually mean 

 lack of sunlight. I understand that at Johns Hopkins 

 Hospital it was found that the two factors mentioned 

 were immaterial if exposure to ultra-violet light was 

 given. It is very doubtful whether massage and 

 electrical treatment have much effect. It is remark- 

 able that the effects ascribed to these are obtained by 

 Rollier in cases which of necessity have to lie quiet, 

 such as tuberculous vertebras, by the action of sun- 

 light alone. The firmness and "tone," even growth, 

 of the muscles is very obvious. 



I doubt whether much advance is likely to be made 

 by obscure references to increase of general meta- 

 bolism as an explanation of the action of ultra-violet 

 light. The dogmatic statement that animal protein 

 is of especial value rests on no good 'evidence. Apart 

 from vitamin-A, diet does not seem of great import- 



NO. 2754, VOL. I IO] 



ance, and even this vitamin may be reduced to a very 

 small quantity in presence of adequate sunlight. 



Should not " vitamin-B " in the seventh line from 

 the bottom of the first column on p. 138 read 

 " vitamin-A " ? And also in the sixth line from the 

 top of the second column ? 



I would conclude that we can reduce the effective 

 factors in the prevention of rickets to vitamin-A and 

 sunlight. It may be found to sunlight alone. 



W. M. Bayliss. 



Iniversitv College, London. 



I am much obliged to Sir William Bayliss for point- 

 ing out my inexcusable mistake of writing " B " for 

 " A " vitamin. One of the advantages of solving the 

 rickets question may be that we shall be able to use 

 a more definitive and memorable nomenclature. 

 " Anti-rachitic " factor is at present plainly in- 

 admissible ; it would be pleasant to call it " Hopkins' 

 stuff," were it not obvious that the identity of the 

 substances which promote growth and have a preven- 

 tive influence on rickets is still an open question. 



On the general question it seems to me that Sir 

 William Bayliss is too ready to accept as a demon- 

 strated fact that ultra-violet light, acting on the skin, 

 produces by a photo-chemical reaction a substance 

 which is equivalent to or identical with the factor in 

 cod-liver oil which influences growth and rickets. It 

 is a very tempting hypothesis because it brings into 

 line a number of apparently discrepant observations. 

 Hut it neglects a great mass of clinical experience 

 which relates the occurrence of obvious rickets to the 

 total intake of food and to 'the influence of exercise 

 and massage. This experience may not be capable of 

 the precise formulation one would like, it may not be 

 of any very high order of observational or experi- 

 mental accuracy, but it has, I think, none the less to 

 be taken into account. It is known too, though here 

 again the data are not beyond criticism, that light 

 increases the rate of genera! metabolism in experi- 

 mental animals. 



The alternative hypothesis suggested in the article 

 seems to have the advantage of bringing all the more 

 or less certain and uncertain data which are available 

 mtii Inn-. What is, of course, needed is a whole series 

 of clinical experiments made with the control and 

 precision of the observations carried out by Dr. 

 Harriette Chick and her colleagues in Vienna. Ex- 

 periments of this kind are laborious and difficult. 

 Meanwhile the practical sanitarian can get to work 

 with sunlight and cod-liver oil and abolish the disease 

 before any one has found out what part of the 

 spectrum is effective. 



The Writer of the Article. 



The Phenomena and Conditions of Sex-change 

 in the Oyster (O. edulis) and Crepidula. 



In Nature of December 15, 1921 (vol. 108, p. 500), 

 I described an experiment from which a sexually 

 mature male oyster was obtained of a maximum 

 age of 23 weeks, from the River Blackwater. In 

 this experiment a fair number of oysters born in 

 192 1 were obtained on specially prepared shells 

 kept isolated in the sea with the view of determining 

 the conditions of sex at a known age at later intervals. 

 With the aid of a Government grant from the Royal 

 Society it has been possible to follow up the experi- 

 ment this year with the following highly interesting 

 results. The young oysters this year were found 

 mostly to be sexually mature or had recently spawned. 

 In one sample of 32 examined from shells on the 

 south shore, River Blackwater, most of the individuals 

 were males, but one large individual (28x31 mm.) 



