ALBUMINS OR PROTEINS. 211 



Even if all the proteins so far investigated are not all derived from the 

 same animal, and the methods of analysis are not so employed as to give 

 exact results, it is, nevertheless, clear that casein must undergo great 

 changes in order to make possible the transformation into these very 

 different products. We have disregarded, to be sure, the other albuminous 

 components of milk, albumin and globulin. It is possible that certain of 

 the proteins in the body are more closely related to these than to casein, 

 at least, as far as their composition is concerned. Such a discovery would 

 not alter our conception, as there can be absolutely no doubt but that 

 the casein plays a large part in the economy of the nursling. This is 

 evident from the large amount present in milk. It might, of course, be 

 objected that casein is mainly utilized as a combustible material, and 

 does not participate to any great extent in the building up of the body. 

 While such an assumption is not yet supported by any proof, still on the 

 other hand, we can reply that our knowledge of the composition of the 

 lactoalbumin and lactoglobulin is such as to warrant the belief that they 

 can only participate to a limited extent in the formation of the albuminous 

 components of the body. They would also have to undergo great changes 

 in order to make them available for the requirements of the cells of the 

 body. 



It is not difficult to imagine the formation of all of the varied albuminous 

 substances from one primitive body, if we take into consideration the 

 fact that a very extensive decomposition occurs even in the alimentary 

 tract. From the complicated albumin, the intestine receives the individual 

 constituents either as such or in long or short chains. The intestine is 

 able to unite these in varying proportions, forming definite products to 

 meet its requirements. The same process can take place in every cell. 



We might expect to obtain an insight into the digestion of the albumins 

 by studying the blood. It were conceivable that the cleavage-products 

 are only recombined in the various organs. Such a conception has much 

 to commend it. We must not, however, forget that the organism strives 

 to maintain a constant composition for its blood-stream. The blood has 

 important functions to fulfill, and any disturbance is accompanied by 

 far-reaching results. It were, in fact, not a matter of indifference to have 

 the various decomposition products introduced into the blood. The cells 

 would require that all the elementary components be brought to them and 

 in definite proportions, in order that they might build up their own albu- 

 mins, a condition of affairs hardly probable with a large part of these 

 components. 



We have not yet succeeded in definitely isolating any peptones or 

 other protein cleavage-products from the blood/ The serum of the blood 



1 E. Abderhalden and C. Oppenheimer: Z. physiol. Chem. 42, 155 (1904). Cf. also 

 P. Morawitz and R. Dietschy: Arch. exp. Path. Pharm. 54, 88 (1905). 



