DEVELOPMENT OF MODERN MEDICINE 45 



bacterial cultures in the laboratory and that this toxin when in- 

 troduced into an animal was capable of exciting the same phenom- 

 ena of disease as the bacteria themselves, was positive proof that 

 bacteria excite disease phenomena at least in some instances by 

 means of a toxin which they form. The elaboration of antitoxins 

 in the body of the infected animal was also promptly recognized, 

 and served to explain not only the self-limitation of many of the 

 infective diseases, but it also helped us to understand the immunity 

 which one attack affords in some of the bacterial diseases. 



Protective Inoculation 



Long before bacterial toxins were recognized as the cause of 

 disease phenomena, Pasteur established the principle of protect- 

 ive inoculation with bacteria of lessened virulence, which was 

 brought about by attenuation of the bacteria by a modification of 

 cultural methods and also by serial inoculation of certain lower 

 animals. This he successfully applied to charbon in sheep and cattle 

 and to chicken cholera. In both of these diseases the bacteria were 

 known and the problems of attenuation could be carried on in the 

 laboratory by direct study of the bacteria before inoculation and 

 afterward when they were recovered from the body of the animals 

 experimented upon. 



His final life-work was no less important in firmly fixing the im- 

 munizing influence in rabies. Here the discovery was made that 

 the infecting bacterium escaped every known means of recognition 

 by microscopical and cultural examination of the tissues and blood 

 of the infected animals. Apparently there are pathogenic germs 

 which we do not know because we have not yet recognized the 

 proper culture material for the successful artificial cultivation 

 of them, nor have we discovered the tinctorial reaction which they 

 may possess; and, finally, it is not improbable that they may be 

 infinitely smaller than other germs and, therefore, more difficult 

 to recognize. 



Pasteur recognized the fact that in hydrophobia the brain and 

 other nervous tissues of an infected animal are capable, when in- 

 oculated into another animal's brain, of producing the disease. 

 That the infected brain used for infecting animals contained the 

 germs which caused the disease was proved by the fact that a 

 stage of incubation occurred in the inoculated animal and that 

 a series of animals were successfully inoculated consecutively from 

 the first. Pasteur then successfully attenuated the unknown micro- 

 organism present in the nervous tissues of an inoculated animal 

 by dessication of the nervous tissue in a sterile apparatus by methods 

 too well known to repeat. Nor is it necessary to occupy time in re- 



