332 



INFECTION AND IMMUNITY. 



Interaction 



of Action of 



Leucocytes 



and Opsoii- 



ins. 



Hypothesis 

 of Welch. 



As pointed out by Glynn and Cox, the work of 

 Wright and his followers has resulted in an undue 

 neglect of the importance of the variation in the 

 power of leucocytosis in the leucocytes themselves 

 as a factor in phagocytosis. They emphasize the 

 fact that while the determination of opsonic power 

 may be an indication of the degree of immunity, 

 it does not represent the phagocytic power of the 

 blood as a whole. In order to ascertain the 

 valuation of the different components separately 

 and as a whole they suggest the comparison of the 

 leucocytes of the blood in question with those of 

 normal blood and call the ratio of the first to the 

 second the cytophagic index. Secondly, they com- 

 pare the action of the leucocytes and the serum 

 of the blood in question with the action of normal 

 leucocytes and serum. The ratio of the first to 

 the second is called the opsonocytophagic index. 



What has come to be known as the hypothesis 

 of Welch is of such practical and theoretical im- 

 portance that reference to it should not be passed 

 'over. It may be put in the form of the following 

 question: If bacterial toxins and the constituents 

 of bacterial cells so act on the tissue cells that the 

 latter produce bodies (antibodies) which are in- 

 imical to the bacteria, why may not the body fluids 

 in turn so act on the bacteria that the latter pro- 

 duce bodies (antibodies) which are inimical to the 

 tissue cells? "Looked at from the point of view 

 of the bacterium, as well as from that of the 

 animal host, according to the hypothesis advanced, 

 the struggle between the bacteria and the body 

 cells in infections may be conceived as an im- 

 munizing contest in which each participant is 



