CHAPTER VIII. 

 THE MANUFACTURE AND USE OF SERA AND VACCINES. 



The most wonderful recent discoveries in the science of bacteriology 

 pertain to the relationship of pathogenic germs and the serum of the blood 

 of susceptible animals. As already stated blood serum has bactericidal 

 properties (see lysins), but it is often not suflEtciently active to destroy certain 

 invading germs (pathogenic) and the disease manifestations, due to the 

 toxins liberated by the germs, gradually develop. The bacterial toxins are 

 of two kinds, those which escape from the bacterial cells and are soluble in 

 the surrounding media, entering the system by absorption; and those which 

 remain within the germ cell and are set free only on the breaking up of the 

 bacterial cells. The former are the toxins proper or exotoxins, the latter 

 are called endotoxins. As already explained the toxins cause the develop- 

 ment within the serum of the blood of certain substances (antibodies), 

 which neutrahze or overcome the effects of the toxins and which are called 

 antitoxins. Investigators hoped that experiments would prove that every 

 pathogenic germ would cause the development of a corresponding antitoxin 

 which might be used in the treatment of the disease. This hope has not 

 been realized. Of the numerous experimentations with antitoxins only one 

 has thus far proven entirely satisfactory, namely, the antitoxin of diphtheria. 

 Several others have proven more or less useful, as will be explaiaed later, 

 but they are far from satisfactory. 



The antitoxins act by neutralizing the bacterial toxins of the disease, and 

 not by acting upon and killing the germs themselves. In this regard the 

 antitoxins or antitoxic sera differ from the antibacterial or bactericidal sera, 

 which act by preventing the development of the bacteria. This distinction 

 and difference is not generally understood. The bactericidal sera have, 

 however, thus far proven quite unsatisfactory in the treatment of disease. 

 They are not standardized by units as are the antitoxins. The dose is by 

 volume, from lo to 50 c.c, and even more, usually given hypodermically. 

 The sera are produced by iajecting increasing amounts of germs (artificially 

 cultured) into the animal, as the horse. As a rule the first injections con- 

 sist of dead germs; finally, living germs of different virulency may be used. 

 By this means a tolerance is established. The serum obtained from animals 

 thus immunized is used in the treatment of disease, its action depending 

 upon its bactericidal properties. There is a group of sera known as com- 



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