ON THE MODE OF ACTION OF PREVENTIVE SERA. 103 



faint clumping power for the cholera vibrio, even in a large dose. 

 The serum taken the day after injection, however, clumped them dis- 

 tinctly, and it was possible to compare its power with that of the 

 preventive serum used for injection. By means of a series of tubes 

 it was found that the serum obtained after injection of cholera 

 serum is only one thirtieth as active as the original cholera serum. 

 For example, in a tube containing 1 c.c. of bacterial emulsion and 

 eight drops of this serum the opacity is the same as that in a tube 

 containing 4 c.c. of bacterial emulsion and one drop of anticholera 

 serum.* In this experiment the same results were obtained as if 

 the 1 c.c. of cholera serum had been diluted in 30 c.c. of liquid. 

 This volume corresponds fairly well to the amount of blood in a 

 guinea-pig of this weight, 360 grams. 



This experiment, moreover, shows why passive immunity cannot 

 be transmitted indefinitely and indicates that the active principles- 

 of the serum are simply diluted in the body without acquiring new 

 and more energetic properties. A word might be added about 

 active immunity. The preventive substances, which are so valuable 

 for animals injected with them, are also evidently equally valuable 

 for those that have elaborated them. It must be admitted that 

 active immunity is evidenced by a perfection of the bactericidal 

 power of phagocytes. t But active immunity has also other 

 characteristics, such as an augmentation of the numberof phagocytes 

 and an increase of chemiotactic sensitivity on the part of leucocytes, 

 as has frequently been recognized by Metchnikoff and clearly 

 evidenced by Massart in his experiments. We cannot, therefore, 

 consider the two kinds of immunity as equally dependent on the 

 presence of a preventive substance. 



* To be sure the clarification took place more rapidly, although no more com- 

 pletely, in the tube containing serum from the passively immunized animal. 

 This is due to the fact that the serum in this tube was in large amount and there- 

 fore acted not only as a diluted preventive substance, but also as a normal serum, 

 and as is well known, normal serum increases the clumping action of preventive 

 serum. The eventual amount of clarification in the two tubes, however, was 

 equal. 



t See article, page 8. 



