1 64 SCIENCE PROGRESS 



that the proteid eaten goes intact to the tissues ; to believe that 

 vegetables " contain the chief constituents of blood . . . ready 

 formed as regards their composition." 



In considering the question further we have, indeed, to 

 recognise more subtle distinctions. It is, at least, probable 

 that the proteids of one species of animal differ from those 

 of others, even as regards homologous tissues ; that the blood, 

 say, of the horse is not, in respect of its proteids, the same 

 as that of the ox ; - and that each of these bloods differs still 

 more from that of man. Evidence is accumulating to show that 

 there is a chemistry of species ; that chemical differences in the 

 protoplasm underlie morphological differences, and that these 

 differences concern, in particular, the complex and easily variable 

 proteids. We see, therefore, that the assimilation of the very 

 diverse nitrogenous materials eaten by animals must be a 

 complex matter, involving, in no small degree, processes of 

 remoulding and modification in order that the normal com- 

 position and specificity of the tissue proteids may appear. 



That a proteid which differs from blood proteids in its 

 fundamental quantitative constitution in the sense discussed 

 above does not enter the blood stream of an animal consuming 

 it with any trace of such deep-seated differences remaining, is 

 strongly suggested by the results of an experiment carried out 

 by Abderhalden and Samuely. These observers bled a horse 

 till the amount of circulating blood proteids was greatly reduced, 

 and then, having withheld food for a time, they fed it upon 

 large quantities of gliadine, the wheat proteid which, as we 

 have seen, contains five times as much glutaminic acid as do 

 the normal blood proteids. After the horse had been kept 

 upon the gliadine, sufficient blood was again withdrawn to permit 

 a further analysis of its proteids. These still exhibited precisely 

 their normal amount of glutaminic acid ; their specific constitution 

 being unaffected by the absorption of the digested gliadine. 



It is perhaps an open question, as will be seen, whether 

 an ingested proteid enters the blood at all in the form of 

 intact proteid molecules. If it does, the experiment just de- 

 scribed seems to indicate that the remoulding and modification 

 spoken of above, occurs at the very first stage of assimilation, 

 and is brought about in the active cellular mechanism of the 

 intestinal walls. 



