ON THE MODE OF ACTION OF PREVENTIVE SERA. 85 



the chance of there being sufficient leucocytes in the cavity when 

 the injection is made to cause the surrounding fluid to become 

 bactericidal, but too few of them to cause phagocytosis on a large 

 scale. This is the essential condition for the production of Pfeiffer's 

 phenomenon. We should expect, then, that if we increase the num- 

 ber of phagocytes at the point of inoculation we should change the 

 appearance of the conflict between the animal body and the infec- 

 tion; and this is indeed what happens. Metchnikoff injected a 

 mixture of preventive serum and vibrios into the peritoneal cavity 

 of a guinea-pig that had received an injection of bouillon the day 

 before; this previous injection caused an increase of leucocytes, so 

 that the vibrios subsequently inoculated encountered large numbers 

 of cells. Under these conditions the vibrios were immediately 

 taken up without any evidence of extracellular morphological 

 change. A morphological change goes on, to be sure, but within 

 the phagocyctes where all the bacteria are to be found.* We 

 have already shown that vibrios are immediately phagocyted when 

 injected into the circulation of vaccinated animals. On the other 

 hand, if the vibrio is injected into a region deprived of leucocytes, 

 for example, subcutaneously, or into an edema area, no extracellular 

 change is found. Phagocytes come up gradually and, as soon as 

 they appear in the infected region, they take up the bacteria which 

 have remained normal. Phagocytosis under these conditions occurs 

 as the initial phenomenon, beginning with the arrival of the cells, 

 and dealing with intact bacteria. 



The experiments which we have just reviewed as well as the 

 conclusions that we have drawn from them have given rise to 

 objections which we must consider. Pfeiffer admits that vibrios 

 are changed in vitro by a mixture of fresh guinea-pig serum and 

 preventive serum, but he thinks that this effect on the vibrios is 

 only passing and not equal in bactericidal force to that which occurs 

 in the animal body. We cannot share this opinion. If vibrios are 

 injected into the peritoneal cavity of an immunized guinea-pig, 

 transformation allowed to take place, and some of the exudate is 

 then withdrawn, it is found on placing it in the incubator that the 



* We do not understand how Gruber could use this experiment to contest the 

 origin of the bactericidal substance from the polynucle'ar leucocytes. (Wiener 

 klinische Wochenschrift, 1896, No. 12, p. 207.) 



