EMPLOYMENT OF BLOOD SERUM 253 



investigator is always actuated by the hope that the particular method 

 he fosters will be of value in the alleviation of human disease, and 

 this fact may determine a subconscious selection of cases and perhaps, 

 equally subconscious, somewhat superior nursing and better care of the 

 cases under special treatment than of the controls. Thus the analysis of 

 statistical evidence must be made with rigid consideration of the various 

 factors of error. Minor differences in percentages of cure or of im- 

 provement may be within carefully computed factors of error and still 

 not take sufficiently into account a considerable factor of error resulting 

 from our ignorance of the intricacy of biological phenomena. 



Immune sera for therapeutic purposes have been prepared by the 

 injection of bacteria, their toxic or non-toxic extracts, or by combina- 

 tions of these substances. Some of these sera exhibit a variable content 

 of antibodies of the first, second or third order of Ehrlich. The most 

 important laboratory test, however, appears to be the protective value 

 of the sera in preventing* infection in animals or their curative value 

 after the infection is established. There is no necessary parallel between 

 the content of special antibodies and the protective or curative value, ex- 

 cept in the case of antitoxic sera. Thus a serum may exhibit a low ag- 

 glutinin or bacteriolysin content and yet protect animals when used in 

 extremely small amounts. The converse is also true, namely, that rela- 

 tively high content of agglutinin or bacteriolysin does not necessarily 

 presuppose a great capacity for protection. Furthermore, it cannot be 

 assumed positively that because animals are protected or cured, the 

 serum will be of equal value in human medicine ; hence the necessity 

 for carefully studied experiments on man. 



Not only have immune sera been employed, but many attempts at 

 treatment of disease by means of normal sera have been made. This 

 procedure is based in part upon the principles of non-specific immun- 

 ological treatment which have been previously discussed. Such sera 

 may be obtained from man, horse, goat, ox or other animal. In the 

 treatment of certain hemorrhagic disease the purpose of the serum 

 may be physiological rather than immunological, inasmuch as the serum 

 is believed to provide certain essentials for the process of clotting which 

 the patient provides in insufficient amounts or not at all. 



In the following discussion it will be noted that there are first taken 

 up those sera prepared by immunization with bacteria; second, those 

 prepared by immunization with bacterial extracts, either with or without 

 the bacterial bodies; third, treatment with the patient's own serum; 

 fourth, treatment with sera from convalescent human cases; fifth, spe- 

 cific serum therapy in diseases of unknown origin, and finally, treat- 

 ment by normal sera. 



SERA PREPARED BY USE OF BACTERIA OR BACTERIAL EXTRACTS 



Anti-streptococcus Serum. The protection afforded by the use of 

 streptococcus immune serum is still problematical. The reason for this 

 lies partly in the fact that there are several different types of streptococci 

 concerned in human infection. Some of the strains occur frequently and 



