HISTORICAL SURVEY 23 



and 1 per cent salt mixture (in the form of corn ash). To his aston- 

 ishment be observed that the animals lost weight and died in spite 

 of the large food intake. The first exact feeding experiments on 

 rats were carried out by Henriques and Hansen (17). The experi- 

 ments were, in the main, of short duration, lasting only from three 

 to four weeks. During this time, the rats gained weight and showed 

 a retention of nitrogen, but the experimental period was apparently 

 too short to discover any food deficiency. Different findings, how- 

 ever, were reported by Falta and Noeggerath (18) who repeated 

 these experiments. They fed various proteins of animal origin 

 together with fat, sugar, starch, salts, lecithin and cholesterol. It 

 was possible to determine the value of the various proteins, although 

 not one of the combinations was permanently sufficient, as was 

 apparent by the poor nourishment to be noted after varying intervals 

 of time. The deficiencies of the diet made their appearance only 

 after prolonged feeding. If the experiment had been terminated at 

 the end of four weeks, the false conclusion could have been made 

 that the diet had been adequate. The food intake was diminished, 

 and the interesting observation was made that the eyes of the rats 

 exhibited pathological changes, of which we shall have more to say 

 later. Working in the laboratory of O. Frank, Jacob (19) reported 

 some feeding experiments with pigeons and rats on a diet which at 

 that time was thought to be sufficient. The pigeons died after a 

 maximum of four weeks with symptoms of severe digestive dis- 

 turbance, although they lived somewhat longer when casein was 

 replaced by meat powder. Rats, on the contrary, lived longer on 

 casein and died after 43, 73 and 125 days. Undoubtedly, the cause 

 of death was the unsuitable composition of the diet, though Jacob 

 considered it to be due to the uniformity and lack of stimulating sub- 

 stances in the diet. The same trend of thought is often met with 

 in the older as well as the newer literature. For instance, 

 McCollum (20) explained the dietary deficiency of synthetic diets 

 as being due to lack of flavoring and stimulating substances, 

 although at present he is the most eager advocate of the new 

 ideas. Through the addition of these flavoring and stimulating 

 substances, he was unable to demonstrate an improvement in the 

 nutritive condition. A very interesting investigation was that made 

 by Watson (21). He fed rats, both young and full grown, on various 

 meat products. The young animals either died very quickly or 



