CHAPTER XI 



SEROLOGY— 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 sufliciently active to destroy cer- 

 tain 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 

 development within the serum of the blood of certain substances (anti- 

 bodies), which neutralize 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 correspond- 

 ing antitoxin which might be used in the treatment of the disease. This 

 hope has not been realized. Of the numerous experimentations with anti- 

 toxins only one has thus far proven entirely satisfactory, namely, the anti- 

 toxin of diphtheria. Several others have proven more or less useful, as 

 will be explained later, but they are far from satisfactory. 



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

 and not by acting upon and kiUing 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 cc, and even more, usually given 

 hypodermically. The sera are produced by injecting toxins or the toxic 

 germs (artificially cultured) into the animal, as the horse. As a rule the 

 first injections consist of dead germs; finally, living germs of different 

 virulency may be used. By this means a tolerance is estabhshed. The 

 serum obtained from animals thus immunized is used in the treatment of 

 disease, its action depending upon its bactericidal properties. There is a 



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