STUDIES ON THE SERUM OF VACCINATED ANIMALS. 47 



tericidal substance in the normal serum acts energetically in the immune 

 serum owing to the action of the preventive substance that accompanies 

 it, increases its power, and lends to it its specific character. 



As a matter of fact it suffices to add a small amount of anti- 

 cholera serum, either fresh or previously heated to 60 degrees and 

 so deprived of its bactericidal property, to normal serum to endow 

 the latter with a very strong bactericidal property. Two liquids then, 

 neither of which is markedly bactericidal, form a mixture that is 

 strongly bactericidal. As we shall later see this bactericidal property 

 is specific and evidenced only toward that race of bacteria used to 

 vaccinate the animal from which the preventive serum has been 

 obtained. It makes no difference in the bactericidal property if the 

 serum is quite clear and without cells or contains only a few cor- 

 puscles. This fact may be expressed in another way by saying that 

 after the preventive serum has been heated its intense and specific 

 property may be restored by adding normal serum. This is brought 

 out by the following experiment : 



EXPERIMENT 14. Normal guinea-pig serum recently obtained 

 was allowed to settle and the upper non-cellular clear fluid was 

 taken off; the lower part of the fluid contained red and white 

 corpuscles. Tubes were made up as follows: No. 1, 12 drops of 

 serum from a goat immunized against cholera (Eastern Prussia) 

 (this serum had been heated for one hour at 58 degrees). No. 2, 

 12 drops of normal guinea-pig serum. No. 3, 8 drops of guinea-pig 

 serum plus 4 drops of goat serum, 58 degrees. No. 4, identical 

 with No. 3 except that the cellular part of the normal guinea-pig 

 serum was used. 



These tubes were then inoculated with a 24-hour culture of the 

 vibrio suspended in 10 c.c. of normal salt solution, and gelatin plates 

 were made at intervals. 



NUMBER OF COLONIES. 



