MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 47 



THE LEUCOCYTE AND BACTERIAL PROTEINS 



But the task of the corpuscles in shielding the tissues against 

 the intrusion of unwelcome proteins in non-assimilable form 

 becomes enormously complicated when the proteins in question 

 are of unfamiliar types and are encased in protective cell walls 

 in other words, when they make up or enter into the bodies 

 of bacterial invaders. As already pointed out, however, the 

 capacity of the leucocyte to engulf these bodies and to digest 

 them and make them part of its own substance is not at all a 

 matter of theory, but a matter of observation under the micro- 

 scope. 



According to the present view, there is no fundamental differ- 

 ence between the digestion of the bacterial proteins and of any 

 other type of protein say a morsel of muscle. There are prac- 

 tical difficulties to be solved, such as getting through the cell 

 wall of the bacterium, but the transformation of its protein, 

 through cleavage, into amino-acids is a process of the same gen- 

 eral type as any other proteolysis. 



As qualifying this statement somewhat, however, it should be 

 borne in mind that no two proteins from different sources from 

 the bodies of different species of animals for example are iden- 

 tical as to all their groupings of molecules. Dr. Nuttall's remark- 

 able precipitin experiments show how marvelously the specificity 

 of proteins holds throughout the animal kingdom. The highly 

 interesting demonstration in the transplantation of organs from 

 one animal to another made by Dr. Alexis Carrel evidence the 

 same thing from a quite different angle. This aspect of the sub- 

 ject is so important, and its bearing in the ultimate problems of 

 protein therapy is so significant, that it will be well to present here 

 a brief review of the two groups of experiments in question, 



TRANSPLANTING ORGANS 



Dr. Carrel has shown that the lost members of a higher animal 

 may be replaced by the substitution of a new member through 

 a surgical procedure. He has amputated the leg of a dog, for 

 example, and replaced the member with a closely similar one 

 taken from another dog; and has seen the new member grow 

 into place and become a part of the body of its new host. 



Dr. Carrel has similarly transplanted various internal organs, 

 including the kidneys, from one animal to another, and caused 

 them to take root, as it were, and perform their normal func- 

 tions. The success of his experiments is due largely to his 

 introduction of a new method of uniting arteries and veins, 

 whereby they are so cleverly sutured together that scarcely a 

 trace of the point of union remains when the wound has healed. 



