156 PRACTICAL METHODS IN IMMUNITY 



serum will not act upon its homologous antigen. This is not true 

 because the complement of human serum invariably haemolyzes the 

 homologous antigen (human red cells). 



The various precipitate tests that have been proposed are unreliable. The 

 precipitate reactions with bile salts give better results than with lecithin, this latter 

 showing positive results in almost one-half of non-syphilitic cases. 



DETERMINATION or OPSONIC POWER AND THE PREPARATION 

 or VACCINES. 



In that which has been considered in the previous pages only the 

 theories of Ehrlich have been brought out. In order to understand the 

 problems involved in the study of opsonins the phagocytic theory of 

 immunity brought forward by Metchnikoff must be studied. Ehrlich's 

 views would seem to hold with diseases where there is an increase in 

 bacteriolytic or antitoxic power of the serum while in such diseases, as 

 are caused by pathogenic cocci, the phagocytic element is operative as 

 there is an absence of bacteriolytic power in the serum of the person 

 with the infection. 



There are two kinds of phagocytes, the microphages (represented 

 by the polymorphonuclears) which on phagolysis or disintegration give 

 off microcytase, a bactericidal substance. Cytase is the same as 

 complement or alexine. 



The microphages are chiefly bactericidal while the macrophages, 

 represented by the large mononuclears of the blood and fixed connective- 

 tissue cells, exert their action on protozoa or animal cells. 



Phagocytes may either act by ingesting bacteria and destroying 

 them intracellulary or they may as a result of phagolysis bring about 

 bacteriolysis extracellularly. According to Metchnikoff the intra- 

 cellular bacteriolysis explains why an individual may possess immunity 

 and yet his serum fail to show any bacteriolytic power. 



The following modification of Leishman's method takes very little time and skill 

 and is applicable in the determination of the organism concerned in an infection, as 

 in Wright's method. The control of vaccine treatment by taking opsonic indices 

 from time to time does not seem to have met with much favor in this country the 

 sources of error being as great, if not greater, than ordinary variations in the opsonic 

 index during the negative and positive phases. 



Method. We start with a i% solution of sodium citrate in salt solution. With 

 this emulsify a twelve to twenty-four-hour agar slant growth of the organism to be 

 tested using 6 to 8 c.c. of the citrated salt solution. The bacterial emulsion is now 



