MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 63 



engulfing the intruder, has given entire protection to its human 

 host. 



Let it be further recalled that this probably would not be true 

 of any cells other than the leucocytes in the entire organism. 



This fact, taken by itself, gives strong corroboration to the 

 thought that the leucocyte is primarily and fundamentally a de- 

 tached organism, acting in close alliance with the animal body, but 

 being in a broad sense independent. 



Of course, the same line of reasoning applies in considerable 

 measure to the red corpuscles as well. And, in both instances, 

 the general idea under consideration finds strong support in the 

 fact that the blood corpuscles of different mammals are histo- 

 logically so similar as to appear practically identical under the 

 microscope. Place a drop of guinea-pig's blood, for example, 

 and a drop of human blood, under the microscope, and not even 

 the trained hematologist can distinguish one set of corpuscles 

 from the other. Even as regards the numerical count, there is 

 striking similarity in case of the red corpuscles ; and the modi- 

 fications in leucocyte count, aggregate and differential, are such 

 as may readily be accounted for by long-established minor differ- 

 ence of dietetic habits modifications, moreover, that may be 

 brought into strict conformity by fluctuations in the human leuco- 

 cyte count under conditions of slight abnormality. 



Obviously, such conformity of corpuscular population in the 

 blood of mammals widely separated in the evolutionary scale, 

 suggests functions of very general and fundamental character, 

 responsive to environmental conditions universally distributed 

 for example, foodstuffs substantially the same, and bacterial in- 

 vaders absolutely identical. 



In this comprehensive view, then, we shall do well to get 

 away from the notion of virulent bacteria, and to think of all 

 the stages of assimilation and immunization as closely allied, 

 and as applying to proteins in general. In practice we must 

 recognize the virulence of certain types of bacteria; but we 

 shall do well to understand this virulence as conditioned merely 

 on the fact that the organism has come somewhat rarely in con- 

 tact with these particular microbes. There are myriads of bac- 

 teria always in the organism and these for the most part are 

 as innocuous as flecks of albumin, for the simple reason that 

 they have been so long with us that they have become domesti- 

 cated that is to say, the body-tissues have become immunized 

 against them. 



According to the Proteomorphic theory, as we have seen, such 

 immunization has resulted in part from the activities of the 

 leucocyte, through which the blood plasma has come to be con- 

 stantly permeated with antidotal chemicals. 



