MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 61 



character of the primitive primordial protozoal ancestor, and 

 which, so far as we can see, is not specialized to perform any 

 other function, is the one which has retained pre-eminently this 

 primordial capacity of harmonizing the organism with the living, 

 or, once living, elements of its environment. 



Such a primitive cell is found in the leucocyte. No other cell 

 in the body retains so fully the primitive characteristics of the 

 protozoal ancestor. And, patroling everywhere the blood stream 

 which carries particles ingested from the outer world, the leuco- 

 cyte is most favorably situated to come immediately into contact 

 with intruding substances, and to take up with the least pos- 

 sible loss of time the work of so modifying them that they meet 

 the needs of the organism. 



The leucocyte looks like an ameba, and it is seen to ingest 

 solid particles of food just as an ameba does. Can we doubt that 

 its chemical processes of digestion are closely comparable to those 

 of its prototype? 



THE LEUCOCYTE AS A MICROCOSM 



At the first thought, it might seem to strain probabilities to 

 the breaking point to suggest that a cell of such proportions as 

 the leucocyte could conceivably be the habitat of a series of chem- 

 ical substances so complex and varied as is here implied. But 

 a very brief consideration of the facts as to the size of mole- 

 cules and atoms, as placed at our disposal by the modern physicist, 

 dispels any such doubts. 



It is known that the smallest particle visible under the micro- 

 scope is about one fifty-thousandth of a centimeter in diameter. 

 Cubing this number, we find that a cubic centimeter will contain 

 one hundred and twenty-five thousand billions of such particles. 

 But the researches of Rutherford, who has somewhat accurately 

 determined the size of the atom, show that a cubic centimeter 

 of space may contain twenty billion times that number of helium 

 atoms. 



In other words, the smallest particle visible under the micro- 

 scope is large enough to contain many times twenty billion atoms ; 

 inasmuch as the atoms computed by Rutherford were in the gas- 

 eous condition, and hence very much more widely separated than 

 those in the solid particle under the microscope. 



It appears, then, that if we were to assume that there are one 

 thousand different antibodies developed in the organism each 

 one antagonistic to some specific type of protein there is ample 

 opportunity for such a collection of antibodies in the smallest 

 particle of matter visible under the microscope, even if we assume 

 that each one of these antibodies is made up of at least twenty 



