48o IMMUNITY. 



described, as it has come into extensive practical use. This 

 observer found that he could intensify the virulence of a strepto- 

 coccus by growing it alternately in the peritoneal cavity of 

 a guinea-pig and in a mixture of human blood serum and 

 bouillon (vide p. 46). The virulence became so enormously 

 increased by this method, that when only one or two organisms 

 were introduced into the tissues of a rabbit a rapidly fatal 

 septicaemia was produced. Streptococci of this High degree of 

 virulence were used first by subcutaneous, afterwards by in- 

 travenous, injection, to develop a high degree of resistance in 

 the horse. Injections were continued over a considerable period 

 of time, and the protective power of the serum was tested 

 by mixing it with a certain dose of the virulent organisms, and 

 then injecting into a rabbit. The serum of a horse highly 

 immunised in this way constitutes the antistreptococcic serum 

 which has been extensively used with success in many cases of 

 streptococcic invasion in the human subject.^ Marmorek, how- 

 ever, found that this serum had little antitoxic power, that is, 

 could only protect from a comparatively small dose of toxin 

 obtained by filtration of cultures. 



Anti-typhoid, anti-cholera,^ anti-pneumococcic, anti-plague, 

 and other sera are all prepared in an analogous manner. 



Properties of Antibacterial Serum. — Within recent years 

 it has been shown that an antibacterial serum, in addition to 

 being protective, may sometimes also present important objective 

 reactions against the corresponding organism, and these are of 

 high importance, as they afford valuable aid in the study of the 

 nature of the preventive power. Of such actions the two chief 

 are the lysogenic and the agglutinative. 



Lysogenic Action. — Pfeiffer found that if certain organisms, 

 e.g. the cholera spirillum, were injected into the peritoneal cavity 

 of a guinea-pig highly immunised against these organisms they 

 lost their motility almost immediately, gradually became granular 

 and swollen up in places into droplets, and then disappeared in 

 the fluid, all these changes sometimes occurring within half an 

 hour — lysogenic action. Further, he found that the same 



^ Results in general are now considered not to be as satisfactory as was at first 

 supposed from the earlier reports of the use of this serum. 



2 A true antitoxic cholera serum has been prepared by Metchnikoff, E. Roux, 

 and Taurelli-Salimbeni. 



