1922] on Vitamin Problems 557 



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 mode- 

 rately 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 ascertained. 

 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 indicates 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 only in infinitesimal 

 amounts. 



The origin of all three vitamins is to be sought in the vegetable 

 kingdom. The production of Vitamin 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 sunflower 

 seeds are almost devoid of it, and so are the 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, however, although very frequent, 



