90 STUDIES IN IMMUNITY 



morphologically intact, but that many of them become motionless 

 and clumped.* 



If a mixture is made of vibrios and normal serum without the 

 specific preventive substance, certain bacteria lose their motility and 

 form round granules; this transformation, however, is only slight. 



It is evident from these facts that the preventive substance immo- 

 bilizes and clumps, and that it becomes still more active when 

 accompanied by the bactericidal substance. Of the two substances 

 the normal bactericidal substance is the only one which alone can 

 cause even a partial morphological change in the organism. It 

 appears probable then "that the preventive substance exerts a 

 certain unfavorable effect on the vibrios, although it is not a real 

 antiseptic ; and that this effect causes them to react more distinctly 

 to the power of the bactericidal substance." 



The origin of this important bactericidal substance which occurs 

 in normal as well as in immunized animals, and also in sick animals 

 or animals that have died of various infections, is known. It is 

 the substance found within the leucocytes, and which even in normal 

 animals is sufficiently concentrated in the cells to bring about a 

 granular modification of organisms ingested by the phagocytic 

 protoplasm. As a result of the coagulation of the blood it is partially 

 liberated in the serum, and gives evidence there of its activity when 

 combined with the preventive substance, although this activity is 

 necessarily weakened by dilution. 



This represented the status of our knowledge a year ago. In a 

 series of recent articles Gruber has carefully repeated the majority 



* It must be noted that this phenomenon of immobilizing and clumping is not 

 nearly so striking with heated serum as with fresh serum. In heated serum, 

 moreover, the vibrios grow rapidly, and after they cease to feel the clumping 

 influence of the serum spread diffusely throughout the fluid. Some time ago 

 Metchnikoff, in his work on the vibrio Metchnikovi, noted that the vibrios grew 

 unclumped in the inflammatory exudate of the immunized guinea-pig, whereas 

 they were agglutinated when inoculated in the serum of the same animal. This 

 offers yet further analogy between the properties of the exudate and the heated 

 serum, which we have already found to be very similar. Both fluids contain 

 (provided they have been taken from immunized animals) the preventive sub- 

 stance; but their bactericidal activity is very much less than that of intact serum. 

 It may also be added that bacteria cultivated in heated preventive serum undergo 

 clumping and granular transformation when a certain amount of normal serum is 

 added to the culture. This addition restores to the serum its original qualities, 

 even after it has served as a culture medium. 



