SOME NEW VIEW POINTS IN NUTRITION 391 



acts especially on secondary proteoses and peptone, breaking them down 

 quickly into amino-acids. This enzyme is naturally present in the 

 intestinal secretions, becomes mixed with pancreatic juice, and is able 

 to reinforce the latter in the complete destruction of the food proteins 

 in the intestine, the final products being simple amino-acids and their 

 combinations known as polypeptides. 



Now, we understand why proteoses and peptone are not normally 

 present in the circulating blood, even of the portal vein. We see that 

 it is no longer necessary to assume a construction of blood proteins 

 from absorbed proteoses and peptone. The old dictum, so often quoted, 

 that the proteins of our muscle tissue, for example, are simple trans- 

 formation products of the various food proteins no longer satisfies us, 

 since it is so out of harmony with observed facts. We see opening up 

 before us a totally different conception of the process of digestion so 

 far at least as it relates to protein food. It has been a long period of 

 time since the discovery of the proteolytic enzyme of the gastric juice 

 by Schwann, or the early work by Claude Bernard on pancreatic juice. 

 Slowly, but surely, however, our knowledge has progressed, until to-day 

 we are on the threshold of a new vista ; new paths spread out before us 

 filled with the light of truth and they bid us hasten to clear away the 

 accumulated misconceptions of the preceding years. 



Think for a moment what the new facts lead to in their bearing on 

 nutrition ! Kecall how we have come to understand that the specific 

 immunities and specific reactions of the blood of different species are 

 properties which reside in the individual blood proteins, and that these 

 peculiarities are associated with the chemical constitution of the pro- 

 teins. Every physiologist knows how greatly blood from different spe- 

 cies varies, and we may safely say that each species of animal probably 

 possesses blood characterized by a personal coefficient in the constitution 

 of its proteins, upon which rests in some measure at least its physi- 

 ological individuality. In the light of such suggestions is it not diffi- 

 cult to conceive of the varying food proteins of our daily diet being 

 merged into the specific proteins of blood and tissue through simple 

 transformation into closely related proteoses and peptones ? Can their 

 individuality be so easily lost by such a superficial alteration ? No, the 

 facts at our disposal to-day clearly indicate that the proteins taken as 

 food can not find a place in the economy of the animal body until (as 

 aptly expressed by Leathes) they have been, as it were, melted down 

 and recast. Stated in different language, it is apparently the purpose 

 of digestion, through the enzymes, pepsin, trypsin and erepsin, to thor- 

 oughly dismember the protein molecule so that no vestige of its original 

 structure remains ; while out of the many fragments or chemical groups 

 so split apart the body can reconstruct proteins adapted to its own par- 

 ticular needs. This means synthesis of a most marked kind, quite 



