July i, 1922J 



NA TURE 



15 



potency is low, the necessary dose of the material to 

 be tested is correspondingly high, and soon transcends 

 what is permissible without interference with other 

 necessary conditions of the diet, such as protein 

 content, etc. Very much the same conditions hold 

 with regard to Vitamin B, especially when this is 

 estimated by the effect of the material on the growth 

 of rats ; and, as a matter of fact, the great bulk of the 

 work carried out in America by this method is not 

 'strictly quantitative, but simply leads to the result 

 that a certain ration does, or does not, suffice for the 

 growth of a young rat. 



As regards Vitamin A the method of Zilva and Miura 

 promises to yield moderately accurate and consistent 

 results. This is attained by keeping the experimental 

 animals (young rats) on a diet totally deficient in 

 Vitamin A until they have ceased to grow, and then 

 ascertaining the minimum dose of the material to be 

 tested which will induce definite and steady growth 

 for four weeks. Animals which do not cease to grow 

 in three weeks are rejected, greater uniformity in 

 the results being thus attained. The test material 

 is, whenever possible, administered quantitatively to 

 the animal and not, as was formerly the practice, 

 mixed with the ration in a known proportion. One of 

 the immediate results of the application of this method 

 has been the discovery that cod-liver oil, formerly 

 classed with butter as a good source of Vitamin A, is 

 in reality 200-250 times as potent as butter and is, 

 along with similar fish-liver oils, by far the richest in 

 this material of all the substances which have so far 

 been examined. 



A further piece of information, which is essential 

 for the detailed study of these substances, is their 

 behaviour towards heat, oxidation, etc. In this 

 respect some progress has been made, and it may be 

 stated with some confidence that both Vitamins A and 

 C are moderately stable towards rise of temperature, 

 provided that air be excluded, whereas in the presence 

 of air they are rapidly inactivated. Whether the 

 effect of air is reversible or not has not yet been ascer- 

 tained. Vitamin B, on the other hand, appears not 

 to be affected by air and is also moderately stable 

 towards rise of temperature. None of the three 

 vitamins is easily inactivated by hydrolysis under 

 anaerobic conditions, and this fact has led to the 

 interesting observation that Vitamin A, although 

 usually associated, in the animal organism, with fat, 

 is not itself a fat but remains in the unsaponifiable 

 residue with almost unabated potency. This in- 

 dicates how small a weight of the vitamin itself is 

 necessary for the daily ration of a young rat. In 

 some cases as little as 1-2 milligram of the oil is sufficient 

 to permit of definite growth, and of this only 1-2 per 

 cent, is unsaponifiable, while, as is well known, the 

 chief constituent of the unsaponifiable matter is 

 cholesterol, which has itself no vitaminic potency. 

 The actual requirement of the vitamin itself must 

 therefore be of the order of 1/500 milligram per diem. 

 The other two vitamins have not been obtained in 

 so concentrated a form, but it appears highly probable 

 that they too are present in foodstuffs onlv in in- 

 finitesimal amounts. 



The origin of all three vitamins is to be sought in 

 the vegetable kingdom. The production of Vitamin 



NO. 2748, VOL. I io] 



A has been followed (Coward and Drummond) from 

 the seed, and it has been found that it does not appear 

 until the photosynthetic processes begin. Thus sun- 

 flower seeds are almost devoid of it, and so are tin 

 etiolated seedlings formed when these seeds germinate 

 in the dark. In the light, on the other hand, the green 

 seedlings, grown in a medium free from the vitamin, 

 produce it freely. This vitamin is often closely 

 associated with the carotene and xanthophyll of 

 plants ; so intimately, indeed, that it was at one time 

 thought that it might be closely related to, if not 

 identical with, one of them. The association, how- 

 ever, although very frequent, is not essential, and no 

 definite relation can be shown to exist between the 

 two. Vitamin C is either absent from seeds or only 

 present in them in very minute amount, but appears 

 when the seed germinates and before any green parts 

 are formed. Nothing is, however, known of the in- 

 active pro-vitamin or of the process by which it is 

 rendered active. 



Concerning the origin of Vitamin B a considerable 

 amount of discussion has taken place. Its presence 

 in a large proportion in yeast points to the probability 

 that it can be produced without the intervention of 

 light, and both in America and in this country it has 

 been found that yeast can actually produce the vitamin 

 when grown in a " synthetic medium " comprising 

 only substances of known composition and free from 

 the vitamin in question. Recently, however, Eijkman, 

 in Holland, has obtained a contrary result, so that 

 this question remains at the moment open. 



The animal organism appears to be unable, in 

 normal circumstances, to produce any of these prin- 

 ciples for itself, and hence the amounts found in animal 

 products depend ultimately on the diet of the animal. 

 This opens up, among many other problems, the im- 

 portant question of the vitaminic properties of milk, 

 and there seems to be no doubt, from experimental 

 work, both here and in America, that these properties 

 are profoundly affected by the diet of the cow. Milk 

 obtained in winter when the animals are stall-fed has 

 been shown to be markedly deficient in Vitamin A, 

 and there is also great danger of a deficiency of Vitamin 

 C. One of the pressing requirements of the moment 

 is the careful quantitative examination of foodstuffs 

 available for the feeding of cattle, so that a rational 

 system of winter feeding can be adopted which will 

 produce milk as good as that given in summer. Such 

 an examination would seem naturally to fall within 

 the purview of the Board of Agriculture. 



The evil results of a deficiency of Vitamins B and C, 

 especially in the diet of children, are well known — 

 beri-beri and scurvy, latent or patent — but the effect 

 of a lack of Vitamin A is not so well recognised or so 

 universally acknowledged. One school considers that 

 a deficiency of this vitamin is at least a prominent 

 factor in the causation, if not, as they formerly held, 

 the sole cause of rickets. Others consider rickets to 

 be a disease brought on by non-hygienic surroundings, 

 lack of fresh air and exercise, etc. The latest experi- 

 mental results show that rickets (in rats) can infalliblv 

 be produced by dietetic changes, but that the lack of 

 Vitamin A does not of itself lead to the disease unless 

 at the same time the diet is faulty as regards the supply 

 of calcium or phosphorus. This faulty mineral supplv 



