122 STUDIES IN IMMUNITY. 



cells present in the peritoneal exudate before injecting bacteria. 

 By means of a simple injection of bouillon a great many active 

 phagocytes may be made to participate at the very beginning of 

 the infection. This method is very useful in studying the course 

 of an infection and we have frequently employed it. 



In order to understand the phenomena of a peritoneal infection 

 in passively immunized animals we must consider a fact evidenced 

 on simultaneous injection of streptococci into a normal and into 

 an immunized rabbit. A virulent streptococcus inoculated into 

 the circulation of a normal rabbit in a dose of 0.1 to 0.25 of a cubic 

 centimeter of culture develops so well as to give an abundant culture 

 from the blood in seven or eight hours. The same dose of culture 

 injected intravenously into a rabbit that has received serum sub- 

 cutaneously is markedly inhibited in growth. A drop of blood 

 taken from any part of the body immediately after injection and 

 inoculated on agar gives rise to a few colonies. Streptococci may 

 still be found in the blood five to seven hours later or even on the 

 following day, but their number is not increased. Such a rabbit, 

 however, succumbs in two, three, or four days, but at autopsy many 

 less bacteria are found in the blood than are present in the rabbit 

 that has received no serum. More bacteria, it is true, are found in 

 the liver, spleen, bone marrow, and particularly in the lung; some 

 of them free and others within leucocytes. 



In this connection we may emphasize the fact that, as a general 

 rule, in rabbits that have received an injection of serum and an 

 excessive dose of bacteria and have survived the controls only two 

 or three days, there are never so many bacteria present in the heart's 

 blood as there are in control animals. The contrast is very marked 

 from whatever region the cultures are made. 



The only exceptions to this rule are those instances where rabbits 

 that have apparently been cured, after a certain time have a fatal 

 relapse, under which conditions the blood may contain nearly as 

 many bacteria as a rabbit infected without serum. 



The peritoneal infection in normal rabbits is accompanied by 

 a rapid invasion of the blood by the micro-organism; the increase 

 of streptococci in the blood is so marked that it, and not the 

 peritonitis, must be regarded as the immediate cause of death. 

 Therefore, since there is less growth of bacteria in the blood of 



