MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 67 



must make similar entrance into the blood stream even more 

 frequently. But if such is the case, we may fairly assume that 

 means will be found there to effect further hydrolyses in the 

 fluids of the body. And, in point of fact, experiments have 

 shown that when certain polypeptids are artificially introduced 

 into the blood stream of animals, they may fail to appear in 

 the excretions, proving that they have been metamorphosed in 

 the body. Abderhalden found that a considerable number of the 

 polypeptids might thus be utilized by the organism of a dog. 



Obviously, then, there may be developed within the body tis- 

 sues or in the blood stream enzymes capable of hydrolyzing the 

 polypeptid molecule a molecule, be it understood, which the 

 combined juices of the stomach and pancreas and duodenum, 

 under ordinary circumstances, are unable completely to cleave 

 or break down. 



The interesting question arises as to what particular tissue or 

 tissues of the body accomplish this remarkable feat. 



Abderhalden set himself the task of experimentally answering 

 this question. In conjunction with Pernuchi, Hunter, and Rona, 

 he prepared extracts and juices of various organs, using Buch- 

 ner's method of grinding up with sand and expressing the juices 

 under a pressure of one hundred to three hundred atmospheres, 

 by which method the cell enzymes are obtained. The tissues 

 thus treated included the liver, the kidney, and the muscles of 

 rabbits and dogs ; lenses from the eyes of pigs ; the brain of the 

 calf; blood serum of ox, rabbit, and dog; and blood corpuscles 

 of various types. Different types of polypeptids were used, to 

 test the selective affinities of the various enzymes. 



It was found that the juices of each and all of the tissues 

 just named (as also juices of germinating wheat, germinating 

 lupine, the mushroom, and various moulds) contain enzymes that 

 hydrolyze one or another of the polypeptids; each juice, as a 

 rule, acting on several different types of polypeptids. Juices of 

 liver, kidney, and muscle hydrolyzed the simpler polypeptids. The 

 plasma and serum of the blood both hydrolyzed complex types of 

 polypeptids, which are known not to be attacked by trypsin, 

 proving that the blood fluids did not receive their enzymes by 

 absorption from the intestinal tract. 



But, in any event, it was needless to look far afield for the 

 origin of the enzymes in the blood fluids, inasmuch as the juices 

 expressed from the red blood corpuscles proved capable of hydro- 

 lyzing the most complex polypeptids. 



The leucocytes of a horse, on the other hand, failed to hydro- 

 lyze a polypeptid which the red blood corpuscles of the horse, 

 and also the blood platelets, hydrolyzed actively. -Blood plate- 



