SOME NEW VIEW POINTS IN NUTRITION 389 



or less diffusible modifications adapted for absorption into the cir- 

 culating blood. The various forms of vegetable and animal proteins 

 supposedly underwent transmutation without much chemical change, 

 into closely allied substances which by simple osmosis or diffusion could 

 enter the circulation and thus be distributed throughout the body. We 

 see in these views a striking example of how preconceived ideas stand 

 in the way of progress. Advance of knowledge is frequently held back 

 by our proneness to interpret observations or data in harmony with our 

 conception of what they should signify. The old-time physiologists 

 knew full well that the protein of the blood and tissues was made good 

 by the protein of the food, and digestion as they understood it was 

 adequate for the purpose, viz., to transform the protein into a soluble 

 and diffusible form. Anything beyond this was not only unnecessary, 

 but uneconomical and wasteful. I well remember an experience of my 

 own twenty-five years ago in Germany when I was at work on the so- 

 called primary and secondary proteoses formed in gastric digestion, 

 substances at that time just discovered as products of digestive action; 

 how an eminent physiologist from Dorpat happened in the laboratory 

 one day, and after looking at some of the products he turned to Kuhne, 

 who was standing near-by and remarked, " It is certainly interesting to 

 see what changes pepsin is capable of producing, but of course they 

 have little bearing on the processes that take place in the stomach and 

 intestine, where naturally the sole aim is to fit protein for absorption." 

 Another eminent physiologist, whose name has long been known to 

 every student of the science, remarked once in my hearing that the 

 acid-albumin stage, the first product formed by pepsin-acid, was as far 

 as gastric digestion need extend, since this substance was easily absorbed 

 and it was a useless waste of energy for protein to undergo conversion 

 into primary and secondary proteoses and peptone. I recall also what 

 controversies arose when it was established that artificial pancreatic 

 juice could break down protein into leucine and tyrosine; those two 

 crystalline amino-acids now so well known as decomposition products 

 of most proteins. When the fact was established beyond a shadow of 

 doubt, physiologists were still disinclined to believe that any appreciable 

 amount of these relatively simple substances could be formed in ordi- 

 nary digestion, because such a view was so strongly opposed to the gen- 

 eral purpose of protein digestion as then held. We were not inclined 

 to follow the path which experiment was opening up simply because 

 our eyes were blinded by preconceived ideas. I recall an early experi- 

 ment made by Kuhne and myself in the Heidelberg laboratory where a 

 dog was fed a large amount of meat and then after a suitable time 

 chloroformed, the small intestine ligatured and the contents analyzed. 

 We found a gram or more of leucine and tyrosine, which we weighed 

 and identified, thus proving to our satisfaction at least that these two 



