204 MICROBES AND TOXINS 



not occur. When phagolysis is thus prevented, the vibrios in all 

 the variations of the experiment possible fail to be transformed 

 into granules but disappear by digestion in the interior of the 

 phagocytes. If we take a guinea-pig strongly immunized 

 against the vibrio of chblera and inject these bacteria directly 

 into its circulation by the jugular vein, we find half-an- 

 hour after no granule transformation in the circulating blood ; 

 the vibrios retain their shape and are to be seen inside the 

 leucocytes. No phagolysis has occurred, accordingly no 

 Pfeiffer's phenomenon, and no extra-cellular destruction by the 

 body-fluids. 



The resistance of the immunized guinea-pig depends so 

 much upon phagocytosis, that if the leucocy tic activity is paralysed 

 by means of a dose of opium, the animal succumbs to a 

 smaller dose of vibrios than is necessary to kill the non- 

 narcotized animal. 



The destruction after phagolysis, Pfeiffer's phenomenon, is 

 not even a general fact. It is true of the cholera vibrio, a 

 fragile bacterium, but even with the typhoid bacillus, also 

 comparatively fragile, it is only a modified Pfeiffer's phen- 

 omenon which occurs. With the bacillus pyocyaneus there is still 

 greater resistance, and greater still with the bacilli of swine- 

 erysipelas and anthrax. In those cases in which the humoral 

 action is imperceptible, phagocytosis is active and constant. 



Opsonins and Bacteriotropins There exist more 



recent theories which, while recognizing the action of the 

 phagocytes, attribute to the body-fluids an important part in 

 immunity : they are said to prepare the bacteria for phagocytic 

 digestion. These preparatory substances or actions are the 

 opsonins of Wright and the bacteriotropins of Neufeld.^ 



^ In their experiments these workers have pursued the same general 

 method ; they have studied the phagocytosis occurring with leucocytes 

 withdrawn from the body and suspended in glass tubes, i.e., the phago- 

 cytosis in vitro already studied in the old experiments of Denys and 

 Leclef. Metchnikoff himself did not fail to compare phagocytosis in 

 vivo and in vitro, having observed the incorporation of the anthrax 

 bacillus by leucocytes suspended in urine and in aqueous humour which had 

 been boiled and thus deprived of all antibodies. 



