486 IMMUNITY. 



Summary with regard to Anti-Sera. In a former 

 chapter it has been shown that in the production of disease 

 by bacteria there are two main factors concerned, viz., the 

 multiplication of the living organisms in the tissues and 

 the production by them of toxines. The facts which have 

 been stated above show that in the blood serum of highly 

 immunised animals there are present substances of remark- 

 able potency, which may act against either of these two 

 factors. In the first place, a serum may protect against the 

 separated toxine, or, in other words, may be antitoxic. 

 In this case there is immunity also against the living 

 organisms, as might naturally be expected ; for when their 

 toxines are neutralised their harmful action on the tissues 

 is removed, and they are then destroyed probably by the 

 same means as ordinary non -pathogenic organisms. In 

 the second place, a serum may lead to the destruction of 

 the organisms. In this case, it is usually indirectly bacteri- 

 cidal, i.e., becomes bactericidal in certain conditions, though 

 in many instances a directly paralysing action on the organ- 

 isms has also been demonstrated. The term antimicrobic 

 is, therefore, conveniently applied to such a serum. In 

 many instances an antimicrobic serum has little or no 

 effect against the toxines ; this is the case with the anti- 

 streptococcic serum (Marmorek), the anti-cholera and anti- 

 typhoid sera (Pfeiffer), and many others. The action of 

 both varieties of anti-sera is, within certain limits, specific, 

 being exerted only against the particular organism or 

 toxine which has been used in its preparation. In the 

 case of both, immunity can be transferred to another 

 animal by means of a certain quantity of the serum, the 

 latter having a definite value which can be ascertained by 

 experiment. It does not follow from what has been said 

 that a serum may not act in both of the ways described. 

 A given serum might, for example, be powerfully anti- 

 microbic and feebly antitoxic at the same time. 



Therapeutic effects of Anti-Sera. As will have been 

 gathered, the human diseases treated by anti-sera are diph- 

 theria, tetanus, streptococcus infection, pneumonia, plague 



