548 INFECTION AND IMMUNITY. 



Thirty minutes after injection of the cocci the 

 exudate in all animals showed an enormous leuco- 

 cytosis. At first they were chiefly mononuclears, 

 but later gave place to polynuclears. In the ani- 

 mals which had received the immune serum, mas- 

 sive phagocytosis had occurred, and in the course 

 of an hour very few cocci were extracellular. On 

 the other hand, practically no phagocytosis had 

 taken place in the animals which had received the 

 normal serum (cited by Neisser). Virulent 

 staphylococci were taken up less readily than 

 avirulent. Such results suggest that the protective 

 power of the serum is due to its ability to stimulate 

 phagocytosis, and this in turn depends on the 

 increased quantity of bacteriotropic substances 

 formed in the serum as the result of immunization 

 (Wright and others) . 



vaccination. In the hands of Wright, vaccination with killed 

 cultures of the staphylococcus has been very suc- 

 cessful in the cure of obstinate cases of acne, fu- 

 runculosis and many other chronic staphylococcus 

 infections. Bouillon cultures are grown for three 

 weeks and then killed by exposure to a tempera- 

 ture of 60 C. for an hour. In order to control 

 dosage, the vaccine is standardized by estimating 

 the number of bacilli in each cubic centimeter. 

 This is done by mixing equal quantities of the 

 vaccine with normal blood, and, after staining a 

 preparation on a slide, determining the ratio of 

 cocci to erythrocytes. There being about 5,000.000 

 erythrocytes to the cubic millimeter in normal 

 blood, the number of cocci is readily reckoned 

 from the ratio which was found. From 2,500 

 millions to 7,500 millions of cocci may be given 

 in an injection. The quantity to be used is 



