534 BIOLOGY OF PNEUMOCOCCUS 



stimulating the production in the horse of antibodies in addition 

 to those commonly found in immune serum. For the purpose, the 

 agar-agar technique of Dochez* (1924), the blood-clot method 

 of Zinsser and Grinnell, 1580 or the procedures followed by Clowes, 

 Jamieson, and Olson, 244 or those of Parker and McCoy 1062 may be 

 useful. 



Dosage. It is difficult to evaluate many of the earlier reports re- 

 garding the dosage of antigens used, since the descriptions re- 

 ferred only to the volume of cultures, extracts, solutions, or other 

 preparations of pneumococci, without any indication of the bac- 

 terial content. There is an optimal range in the amount of vaccine 

 which will induce satisfactory antibody production without caus- 

 ing harmful effects in the animal. Landmann (1908) 779 observed a 

 greater loss of horses following increases in dosage. When living 

 cultures are used for immunization the doses cannot be increased 

 as rapidly as when killed antigens are used (Neufeld and Haendel, 

 1909 989 ). Avery and his associates 36 stated that "doses should be 

 small, as very large doses inhibit the immunity response." The au- 

 thors recommended that the heat-killed suspensions used for injec- 

 tion should contain about 200 to 300 million organisms per cubic 

 centimeter and the dose should represent the bacteria from 50 

 cubic centimeters of culture; with living organisms, the first injec- 

 tion consisted of the organisms from 2.5 cubic centimeters of 

 original culture. Doses were usually doubled progressively if the 

 reaction of the horse was favorable until the maximal dose consist- 

 ing of the sediment from 300 to 400 cubic centimeters of broth 

 culture was administered. 



In a study of the immune response of rabbits to prolonged im- 

 munization with vaccines of Type I Pneumococcus, Barnes and 

 White 86 determined the density of the bacterial suspensions as a 

 measure for regulating dosage. Based on the experience thus 

 gained, the present practice of the authors in immunizing horses is 

 as follows: All vaccines are standardized by means of the Gates 



* Personal communication. 



