INFECTIOUS DISEASES. 617 



blood of an infected animal. To-day no one questions the etio- 

 logical relation of Bacillus anthracis to the disease anthrax. And 

 this bacillus has served for innumerable experiments relating to 

 the solution of a variety of questions in pathology and preventive 

 medicine. Among these we may mention the following, each of 

 which has an extended literature : attenuation of virulence ; pro- 

 tective inoculation of susceptible animals ; hereditary transmis- 

 sion of protection; passage of pathogenic bacteria through the 

 placenta, from the mother to the foetus ; explanation of acquired 

 immunity ; comparative value of germicidal agents and of anti- 

 septics ; conditions governing spore formation, etc. 



Proceeding with our historical review : In 1873, Obermeier, a 

 German physician, announced the discovery, in the blood of pa- 

 tients suffering from relapsing fever, of a minute, spiral, actively 

 motile micro-organism the Spirochete Obermeieri which is now 

 generally recognized as the specific infectious agent in this dis- 

 ease. Recently (1890) a spirillum closely resembling the relaps- 

 ing-fever spirillum has been discovered by Sakharoff, a Russian 

 investigator, in the blood of geese. The investigations of the 

 author named show that it is the cause of a fatal epidemic disease 

 which occasionally prevails among geese in certain swampy 

 localities in Caucasia. 



In 1879 Hansen reported the discovery of bacilli in the cells of 

 leprous tubercles. Subsequent researches have shown that this 

 bacillus is constantly associated with leprosy, and presumably 

 bears an etiological relation to the disease. 



In the same year (1879) Neisser discovered the " gonococcus." 

 The bacillus of typhoid fever was first observed by Eberth, and 

 independently by Koch, in 1880, but it was not until 1884 that 

 Gaffky's important researches relating to this bacillus were 

 published. It is now well established that this bacillus is con- 

 stantly found in the spleen and intestinal glands involved in 

 cases of typhoid fever ; and pathologists have generally accepted 

 it as the specific etiological agent in this disease. We can scarcely 

 doubt the correctness of this conclusion, although it must be ad- 

 mitted that no satisfactory experimental demonstration of the 

 fact has yet been made, inasmuch as none of the lower animals 

 are subject to the disease as it occurs in man, and inoculations 

 with pure cultures do not give rise to identical morbid phe- 

 nomena. Since the discovery of the typhoid bacillus very numer- 

 ous researches have been made to determine in an exact manner 

 its biological characters, its resistance to germicidal agents, the 

 duration of its vitality in drinking-water and in the soil, its pres- 

 ence in water the ingestion of which has been suspected of caus- 

 ing typhoid fever in man, etc. As to the results of these in- 

 vestigations we may say, in brief, that it has been shown that the 



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