MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 53 



of antibodies. These specific antibodies are no mere by-products 

 of the cleavage of the foreign proteins, as was once supposed. 

 They are chemical compounds put forth by the defensive mechan- 

 ism and having such specific properties as will enable them to 

 antagonize the particular protein that evoked them. This is 

 equally true of proteins of every type of the molecules that 

 make up the most wholesome foodstuff, no less than of those 

 that make up the most virulent bacillus. 



The chemicals in question are known as bactericides, bacterio- 

 lysins, hemolysins, agglutinins, precipitins, and opsonins. Some 

 of these names may be duplications, but the existence of a cer- 

 tain number of what may conveniently be termed "antibodies," 

 developed through response of the organism to the intrusion of 

 the foreign proteins, is a chemical fact supported by unassailable 

 evidence, quite apart from any theory whatever as to the pre- 

 cise bodily mechanism through which they are produced. We 

 have just seen this illustrated in detail in the case of Dr. Nut- 

 tail's precipitins. 



But when we attempt to localize this mechanism, we find our- 

 selves at once involved in difficulties. To be sure, the line of 

 reasoning just presented seems to point rather clearly to the leu- 

 cocyte as the developer of the antibodies; inasmuch as that cell 

 is known to be the digester of the offending protein itself. But 

 if we seek direct proof, we find the evidence not altogether 

 convincing. Nevertheless a number of observations have been 

 recorded, as to the result of direct experiments, that are at least 

 highly suggestive. 



Thus, for example, Ruffier and Crendiropoulo, as cited by Nut- 

 tall, found evidence that agglutinins may exist in the leucocytes 

 of rabbits and guinea pigs, inasmuch as an extract of leucocytes 

 from an immune animal had greater agglutinating power than 

 did the same animal's serum. The observations of Metchnikoff 

 convinced him that the output of "fixatives" varies directly with 

 the degree of phagocytosis. Gengou, following up Metchnikoff's 

 conception at the Pasteur Institute, "concluded that the hemo- 

 lysins are derived from leucocytes, for the reason that plasma 

 separated from fresh blood, when cooled throughout, by cen- 

 trifugalization, was less hemolytic than serum." The experiments 

 on which this last conclusion were based were repeated, however, 

 by Ascoli, with opposite results, and Pfeiffer and Marx found 

 antibodies less abundant in the ground bodies of leucocytes of 

 immunized animals than in the plasma. 



Again, according to a recent analysis of Gay and Rusk, "the 

 work of Deutsch, Castellani, Rath, Weil and Braun, and Kraus 

 and Schiffmann all shows that the agglutinins appear in the 

 blood serum before they are present in the extract of any organ." 



