240 PASSIVE IMMUNIZATION 



cytosis and phagocytosis, while the organisms multiply without any 

 very evident restraint, the treated animals show exactly the opposite 

 picture, i. e., extensive hyperleukocytosis and phagocytosis without 

 evidence of multiplication. The same can be shown outside of 

 the body, directly under the microscope; for whereas in the presence 

 of normal serum, washed leukocytes will scarcely take up any viru- 

 lent streptococci, they do so readily when in contact with immune 

 serum. 



Whether or not bacteriolytic processes also play a role in the 

 protection of the animal with suitable immune sera is still a matter 

 of dispute. Antitoxins, on the other hand, certainly are not present. 



Preparation and Standardization. The preparation of the antistrep- 

 tococcus sera is conducted essentially on the same lines as that of 

 other non-antitoxic sera, viz., by starting the immunization with 

 small doses of killed-off cultures and progressively increasing the dose, 

 until finally full virulent living organisms can be injected. At the 

 Serum Institute of Vienna, bouillon cultures of from two to eight 

 days' growth are used, the initial dose being 0.5 c.c., and the final 

 one varying between 100 and 200 c.c., all the injections being given 

 subcutaneously. The animals are not bled until the immunization 

 has been continued for about six months. The serum is then tested 

 in reference to its bacteriological purity and titer, and finally put up 

 in doses of 50 and 100 c.c. each, without any preservative. 



In making up the polyvalent antigen for immunization, it is con- 

 venient, even though all the other strains be of human origin and 

 passed through animals; to introduce one strain which has been so 

 treated and brought to a high degree of virulence, for mice for 

 example, so as to have an approximative indicator at least for the 

 potency of the antiserum, this being then standardized against that 

 particular "animalized" strain. At the same institute that dose 

 of streptococci which will kill a white mouse at the expiration of, or 

 just preceding the end of four days, is designated as a single lethal 

 dose; but in testing an antiserum, ten times this amount is chosen 

 as the dose against which one unit of antiserum should afford pro- 

 tection. A single normal serum is one of which 0.01 c.c. will afford^ 

 this degree of protection, and 1 c.c. of such a serum is said to con- 

 tain a single immunization unit, and 1 c.c. will accordingly protect 

 1000 mice against a single lethal dose each. The Vienna serum, as 

 it is now marketed, contains 20 to 40 units to the cubic centimeter. 



