IO FEEDING EXPERIMENTS WITH ISOLATED FOOD SUBSTANCES. 



in the form of the "artificial" mixtures. The danger of drawing 

 erroneous conclusions is attested by the fact that he was unable to 

 maintain his rats upon a variety of food articles : dog biscuit, graham 

 bread, rice, etc., which one would assume to be adequate as mixed 

 food. 



In explanation of his failures he says: 



Der Grund liegt hauptsaehlieh darin, dass die Thiere bei der reizlosen 

 einformigen Kost den Appetit verlieren, im geringeren Grade wohl aueh 

 darin, dass die Nahrung mit zunehmender Appetitlosigkeit im Darm auch 

 weniger gut ausgeniitzt wird. (p. 168.) 



It might have been expected that the difficulties here encoun- 

 tered could be obviated by the use of animals in which forced feeding 

 could be satisfactorily instituted. C. Voit* kept a pigeon alive 124 

 days with peas by this method. Jacob! failed in repeated trials with 

 pure food mixtures, and attributes his lack of success to the impos- 

 sibility of adapting the physical texture of the introduced pure-food 

 pellets to the requirements of the avian digestion apparatus, so that 

 the pigeons died of inanition. He also attempted to advance beyond 

 his predecessors in feeding "artificial" mixtures (with casein as the 

 sole protein) to rats. He was scarcely more successful; the animals 

 ate sparingly and he concludes that if it is possible to keep an animal 

 alive 124 days, as he did, on a diet of the character noted, this 

 must contain all the substances essential to life. The animals did 

 not exhibit any gross pathological defects at autopsy, but all visible 

 fat had disappeared. The next attempt, Jacob optimistically sug- 

 gests, must be directed toward devising combinations which the ani- 

 mals will eat: 



So gelingt es vielleicht doeh, eine Nahrung aus reinen Nahrstoffen ohne 

 Genussmittel herzustellen, welche alle zur dauerndenErhaltungeinesTieres 

 notigen Stoffe im richtigen Mengenverhaltnis enthalt. (p. 60.) 



McCollumJ fed both young and full-grown rats on complex 

 artificial mixtures, in which edestin, zein, and sometimes casein, 

 were the sole sources of nitrogen. They are the most successful 

 experiments yet reported as regards maintenance of body-weight or 

 growth on a restricted quality of protein intake. The chief difficulty 

 encountered was that of anorexia, which the author attempted to 

 overcome by frequent changes in the combinations of food-stuffs 

 used and by addition of flavors. Some of the trials extended over 

 more than 100 days without death; but the rats failed to maintain 

 their weights, even with the most persistent coaxing of the appetite. 

 Data regarding the food intake are wanting, so that the inanition 

 factor (due to deficient calories) can not be excluded. 



*Voit: Zeitschrift fiir Biologie, 1866, II, p. 64. 



t Jacob: Zeitschrift fiir Biologie, 1906, xlviii, p. 19. 



+McCollum: American Journal of Physiology, 1909, xxv, p. 120. 



