STUDIES ON THE SERUM OF VACCINATED ANIMALS. 53 



containing serum the white corpuscles penetrate more deeply and 

 are more scattered. This difference in appearance is probably due 

 to the fact that in the serum the leucocytes find a suitable non-toxic 

 medium that allows them to remain motile for a longer period. 



(6) Tubes were placed in the peritoneal cavity of a normal 

 guinea-pig and withdrawn after 12 hours. 



No. 1. Agar culture of Massaouah suspended in 10 c.c. of salt 

 solution and sterilized. Strong attraction for leucocytes. 



No. 2. Serum of a rabbit immunized against Massaouah. Marked 

 attraction. 



No. 3. Serum of a normal rabbit. Very slight attraction. 



No. 4. Salt solution of 0.65 per cent. No attraction. 



These experiments show that preventive serum has a much more 

 marked chemiotactic influence than normal serum. It may be 

 asked whether the leucocytes of a vaccinated animal are attracted 

 by its own serum. That such an attraction takes place is shown 

 by the following experiment: 



(c) A specimen of blood was taken from a guinea-pig weighing 

 420 grams that had been well vaccinated against the vibrio of 

 Massaouah. Two days later the serum was put in tubes which were 

 placed in the peritoneal cavity of the same animal. 



No. 1. Agar culture of the vibrio Massaouah suspended in salt 

 solution. Strong attraction for the leucocytes. 



No. 2. Serum from a normal guinea-pig. Faint attraction. 



No. 3. Serum from the animal used in the experiment. Very 

 distinct attraction. 



The following experiment also shows that cultures of cholera 

 vibrios will attract leucocytes even when they have been suspended 

 in a rather large volume of salt solution. 



(d) A normal guinea-pig was used. 



No. 1. Massaouah culture on agar 24 hours old suspended in 5 c.c. 

 of salt solution. Strong attraction. 



No. 2. The same culture suspended in 100 c.c. of the same solu- 

 tion. Strong attraction. 



No. 3. Same culture suspended in 200 c.c. of the solution. Very 

 distinct attraction. 



Considering these experiments collectively it is to be noted that 

 the serum of a normal rabbit or guinea-pig has only slight attraction 



