CH. XLL] VITAMINES 627 



all three. The synthetic activities of the animal body, or the possi- 

 bility of the transmutation of one amino-acid into others are thus 

 clearly brought to mind. 



My next example may be taken from an animal higher in the 

 scale. A food-mixture in which gliadin was the only source of 

 nitrogen was given to a puppy in place of its mother's milk ; this 

 produced typical failure in growth. Nevertheless the mother dog 

 thrived on the same diet and actually produced young, and secreted 

 milk in sufficient quantity and quality to induce normal growth in 

 her offspring. No stronger proof could be adduced of a power in the 

 adult body to synthesise "Bausteine" which are absent from the 

 food. The liver cells have been usually credited with the main share 

 in such marvellous synthetic power ; but there is a reaction in the 

 minds of physiologists just now against this tendency to pile up 

 hepatic duties. Several pieces of work show that, although the liver 

 doubtless does its due share of the work, other tissues and organs 

 also participate in it. 



The only other example I select from the large mass of material 

 at hand illustrates the importance of those unknown but indispens- 

 able constituents of a diet which are referred to in our chapter on 

 Foods (p. 491). An animal, or at any rate a growing animal, cannot 

 live on protein alone, even if it is mixed with appropriate mineral 

 salts, and with a proper supply of fat and carbohydrate to supply 

 the necessary energy ; these other organic compounds of uncertain 

 nature are absolutely indispensable. F. G. Hopkins was one of the 

 earliest to recognise the importance of what, for want of a better name, 

 we may term these accessory factors in a dietary, and the effect of 

 quite small quantities of such substances is admirably illustrated in 

 his most recently published work. Groups of young rats were fed 

 on a diet of caseinogen, fats, carbohydrate, and salts, and compared 

 with other rats on the same diet, plus a minute ration of fresh milk. 

 The former soon ceased to grow; the latter grew normally. The 

 consumption of food was practically the same in all the animals, but 

 the milk addendum reduced the food necessary for a given increment 

 in weight to one-half or less. Moreover, cessation of growth occurred 

 before there was any loss of appetite to account for it. What the 

 actual substances are in the milk which thus markedly, although in 

 a secondary way, affect growth is not yet known. We can therefore 

 only surmise that the unknown material (provisionally termed 

 vitamine) may contain some particular "Bausteine" which the 

 animal body is not able to build up for itself ; or it may be that the 

 effect is due to a stimulating effect upon the cell-protoplasm which 

 leads to the development of the necessary synthetic power. Funk 

 has suggested that the " vitamines " are derivatives of pyrimidine. 



