210 OPSONINS 



is no phagocytosis. On the other hand, when the bacteria are kept 

 in contact with the immune serum, then washed and brought in 

 contact with the leukocytes, active phagocytosis begins. This shows 

 that the serum of an animal immunized to a streptococcus, for instance, 

 does not stimulate the leukocytes but in some way makes the strepto- 

 cocci more inviting as a food. 



Parenthetically it should be stated that there are substances which 

 stimulate phagocytes, such as nuclein, peptone, quinin, potassium 

 iodid, etc., but these have nothing to do with opsonins. Anesthetics 

 inhibit phagocytic action and the same is true of narcotics. 



The study of phagocytosis in vitro has shown that the immune 

 serum and the leukocytes need not come from the same animal, not 

 even from the same species. Hektoen has shown that immune sera 

 from horses, dogs, rabbits, guinea-pigs, etc., prepare streptococci so 

 that they are readily devoured by leukocytes from man. This list of 

 animals has been extended by Hektoen's students so that it includes 

 certain cold-blooded ones. Streptococci sensitized with immune sera 

 from warm-blooded animals are readily devoured by phagocytes from 

 cold-blooded ones. This makes it all the more certain that the reaction 

 is between the serum and the bacteria. When the latter are prepared 

 by the former, a phagocyte from any kind of an animal will eat them. 



The opsonins do not kill the bacteria; indeed, they do not stop 

 their growth nor lessen their virulence. When bacteria have been in 

 contact with homologous immune sera long enough to be sensitized 

 and are then placed in ordinary culture media, they multiply, and 

 their progeny are not found to be sensitized. We infer that the union 

 between cell substance and opsonin has no destructive or radical effect 

 on the former. In fact, Hektoen has shown that anthrax bacilli, strep- 

 tococci and pneumococci grow abundantly in homologous immune 

 sera. 



Phagocytosis proceeds in the same way in vitro and vivo. The 

 serum from a rabbit immunized to streptococcus, will sensitize the 

 streptococcus in a test-tube or in the abdominal cavity of a guinea- 

 pig, and a healthy phagocyte from any source will eat the prepared 

 food in either place. Indeed many bacteria are more readily disposed 

 of by the phagocytes in test-tubes than in the body, because in the 

 latter they develop in the second and subsequent generations, protec- 



