666 LECTURE XXIX. 



squirrel crystallizes in the hexagonal system, and that of the mouse in the 

 orthorhombic. From a mixture of these two kinds of blood, each crys- 

 tallizes in its own specific form, and to the same extent as corresponds to 

 the original mixture. 



Comparative quantitative analyses of different kinds of blood l indicate 

 that, within fairly narrow limits, there is a definite composition of the 

 blood for every species. In closely related animals the relative amounts 

 of the individual constituents are similar, while in unrelated ones the differ- 

 ences may be very marked. It is noteworthy that the serum appears to 

 be of very similar composition in the case of all mammals. The product 

 in this case is apparently identical when prepared from various classes of 

 different animals. We must not forget, however, that the examination 

 of the ash can give us at best only a rough idea of the composition of the 

 serum. It only serves to tell us what elements are present, and nothing 

 at all concerning the manner in which they are contained in the circulating 

 blood. But even if it were possible to prove that the inorganic and simple 

 organic constituents were qualitatively and quantitatively the same in 

 the sera of widely different species, there still remains the far more difficult 

 problem of determining the identity of the proteins. It is perfectly possible 

 that the different proteins in the blood contain groupings which are char- 

 acteristic of each species of animals. 



Let us return to the oft-discussed observations concerning digestion. 

 We have seen that the nature of the proteins contained in serum 2 is evi- 

 dently independent of the kind of food that is eaten. This is probably 

 true for all the other substances, or at least for the more complicated 

 organic ones. The cells of the body never know what the nature is of the 

 food eaten. They always receive a modified nutriment. The ferments 

 of the intestine and the accessory glands have the function of resolving 

 the complicated organic constituents of the food into cleavage-products 

 and, on the other hand, the cells of the intestine have the property of effect- 

 ing a chemical reorganization of these building-stones into new products 

 which are suitable for the cells of the body. The intestine thus regulates to 

 a certain extent the general metabolism and guarantees the maintenance 

 of a constant composition of our tissues. It is, therefore, perfectly clear 

 that the entire course of the metabolism in the cells of our organs is depend- 

 ent upon their composition. The composition of the protein molecule, 

 or perhaps better the protein molecules, is particularly influential in impart- 

 ing to each individual cell its characteristics. The cells of the body pro- 

 duce the ferments, and these are probably transformation products of 

 the proteins. We can easily understand that their finer construction is 



1 Emil Abderhalden: Z. physiol. Chem. 23, 521 (1897); 25, 65 (1898). 



2 Emil Abderhalden and Franz Samuely: Z. physiol. Chem. 46, 193 (1905). Cf. 

 Lecture X, p. 212. 



