1 8 THE PHYSIOLOGY OF PROTEIN METABOLISM 



of the tissues. After feeding with hemielastin (artificially prepared) 

 he found evidence of its presence in the blood, liver, spleen, muscle, 

 stomach and intestinal wall. Later he fed elastin itself and thus al- 

 lowed the elastin proteose to be formed in the normal course of diges- 

 tion and confirmed his observation that the proteose could be detected 

 in the blood and the tissues. It was not confined to the portal blood, 

 but was also found in the systemic (carotid) blood. Abderhalden and 

 Ruehl (38) were quite unable to confirm this work of Borchardt al- 

 though they took every precaution and care. They found no trace of 

 the hemielastin in either blood or tissue. They stated further that 

 as a source of protein supply elastin could not be considered as it was 

 very poorly absorbed. They admitted that it might, however, have a 

 slight protein sparing action. Freund (141) maintained that the ex- 

 planation suggested by Abderhalden and Oppenheimer was wrong, 

 that the biuret reaction was due simply to imperfect coagulation. He 

 held that Abderhalden by his method not only precipitated the proteins, 

 but also every trace of proteose (Abderhalden 6). Finally Kbrosy (225) 

 using the most modern and careful methods and Howell (204) using 

 a method of dialysis where all protein was held back, were quite un- 

 able to detect the presence of proteose and peptone in the blood, even 

 at the height of digestion. Abderhalden and Pincussohn (35) have 

 further found that, after the injection of peptone, a ferment appeared 

 in the plasma capable of decomposing the injected material. If pep- 

 tone were a normal constituent of the blood it would be expected that 

 the ferment would also be constantly present but such is not the case. 

 The conclusion must be reached that there is no very decisive evi- 

 dence in favour of the presence of either proteose or peptone in the 

 blood. If it be present, it must be merely in traces. 



Fate of Protein after Absorption. 



If the view be untenable that the protein enters the organism 

 from the intestine in the form of proteoses and peptone in what form 

 does it enter? At present there is a very marked difference of opinion 

 on the question. One set of workers claim that immediately after 

 absorption the products of digestion are synthetized to a coagulable 

 protein, whereas the other set maintain that the absorption takes place 

 in the form of very simple protein products either as simple amino 

 acids or groups of these and that it is in this form that protein is 

 conveyed in the blood stream, allowing each tissue to choose for itself 



