96 sri i>n:s in immunity. 



If those substances in sera which clearly and actively cause the 

 immobilization and clumping of a given bacterial species are to be 

 found in the serum of a vaccinated animal; and if the clumping by 

 a specific serum occurs only with bacteria which arc similar to those 

 used to vaccinate the animal from which the serum is derived, and 

 if, thirdly, bacteria of the same species always act in a similar man- 

 ner with a given scrum; we may then regard as exact diagnoses 

 based on clumping alone, without considering such other characters 

 as granular transformation. Not all these conditions, however, are 

 realized. 



First : — Clumping of bacteria may be produced by sera other than 

 specific preventive sera; for example, normal horse serum clumps 

 cholera vibrios energetically. A similar, though slightly feebler 

 effect, is produced on the vibrio Metchnikovi; it also happens fre- 

 quently with B. tetani, B. coli and B. typhosus and less distinctly 

 with the streptococcus (the culture used was very virulent).* This 

 property persists in horse serum that has been kept or heated for 

 half an hour to from 60° to G2° C. ; under this latter condition, how- 

 ever, the property is somewhat diminished. 



If two drops of horse serum are added to 1 c.c. of an emulsion of 

 vibrios (a 24-hour agar culture suspended in 20 c.c. of normal salt 

 solution) the bacteria fall rapidly to the bottom of the tube and 

 the supernatant fluid becomes absolutely clear within two hours. 

 The clumping property, then, is well developed in horse serum, and 

 much better developed relatively than is the immobilizing property. 

 For it is found on examining hanging drop preparations from the 

 emulsion of vibrios and serum, that there are vibrios which, although 

 brought together in definite masses, have not entirely lost their 

 motility; these motile vibrios, moreover, frequently cause a move- 

 ment or turning of the entire mass. These facts may be noted even 

 when a large amount of serum is employed. But if such mixtures 

 have been made according to Gruber's method in test tubes, the 

 deposition of bacteria is complete, as clumps fall to the bottom in 

 spite of their oscillating movements. Although the specific preven- 

 tive serum of the immunized guinea-pig gives complete immobili- 

 zation more easily, horse serum produces the same effect on the 



* Normal guinea-pig serum has practically no effect on these different 

 bacteria. 



