xii, B,5 Schobl and Monserrat: Fixation Test for Syphilis 251 



serum averaged 100 units per cubic centimeter, rarely 150, and 

 never more than 200 units per cubic centimeter. Simultaneous 

 intravenous and intraperitoneal injections gave the best results. 

 Allowing an interval of four days between injections, from 10 to 

 15 cubic centimeters of serum were obtained in twenty-six days. 

 That is to say, one rabbit yielded from 1,000 to 1,500 units. 

 However, sera of not more than 50 units per cubic centimeter 

 were frequently obtained. Considering the high mortality of 

 the treated animals and the poor condition of the survivals, it 

 will be appreciated that the production of antihuman haemolytic 

 amboceptor requires a great many animals and involves a good 

 deal of work, time, and expense. 



Following are the records of animals immunized with monkey's 

 red corpuscles. 



Rabbit 1 received the usual number of injections of washed 

 monkey's red cells, that is, five injections intravenously and five 

 injections intraperitoneally at the same time. The period of 

 immunization extended over fifteen days. Five days after the 

 last injection the animal was bled. Two days later another 

 bleeding was taken from the heart. Altogether 25 cubic centi- 

 meters of serum were obtained by both bleedings. The mixture 

 of the two sera tested 4,000 units per cubic centimeter. The 

 total amount of monkey's blood used for immunization was 7.30 

 cubic centimeters. This rabbit, three weeks after the immuniza- 

 tion began, yielded 100,000 units and survived, thus being avail- 

 able for other purposes. 



Rabbit 2 received three injections within eight days. The total 

 amount of blood injected was 4.50 cubic centimeters. Five days 

 after the last injection the serum of this animal tested 2,000 

 units per cubic centimeter. 



Rabbit 3 received only two injections of monkey's red cells. 

 The total amount of blood was 2.50 cubic centimeters. Its serum 

 tested 100 units per cubic centimeter. 



Rabbit 4 received but one injection of monkey's red cells. 

 When tested five days after the injection, the serum had a titer 

 of less than 20 units per cubic centimeter. 



Following the usual scheme of immunization, in rabbit 1 a 

 serum was obtained in three weeks, which was twenty times 

 higher than the best average antihuman haemolytic serum; in 

 rabbit 2 ten times higher serum was obtained in two weeks j 

 and rabbit 3 yielded in nine days serum of the same titer as the 

 average antihuman amboceptor obtained after five injections. 



Rabbit 4, after one injection, gave serum of 20 units per 

 cubic centimeter. 



