6 APPLIED BACTERIOLOGY 



bears his name, in the blood of patients suffering from 

 relapsing fever. Hansen in 1879 described the bacillus of 

 leprosy. In 1880 Eberth discovered the typhoid bacillus, 

 which was artificially cultivated by Gaffky in the following 

 year. Koch in 1881 devised his beautiful method of 

 using solid culture media, which is now so universally 

 used. He thickened nutrient meat-broth with gelatine, 

 whereby the organisms inoculated into the liquid are fixed 

 in situ when it cools and sets, thus rendering it easy to 

 obtain pure cultures of any micro-organism by picking out 

 a fragment of a colony and planting it on a fresh surface. 

 Loffler in 1882 discovered the organism of glanders. In 

 1883 Nicolaier described and investigated the bacillus of 

 tetanus, Klebs and Loffler the bacillus of diphtheria, and 

 Koch the bacillus of tubercle. Koch, again, in 1884 published 

 his discovery of the spirillum of Asiatic cholera (Koch's 

 comma bacillus). The specific organism of influenza was 

 discovered simultaneously by Pfeiffer, Kitasato and Canon 

 in 1892, while, perhaps, the latest discoveries of importance 

 are those of Bubonic plague, by Kitasato and Yersin, 

 during the epidemic at Hong Kong in 1894, and of yellow- 

 fever by Sanarelli in 1897. 



Twenty years ago it would have seemed chimerical to 

 have said that we could cultivate at will, in the laboratory, 

 the very living essence and cause of such diseases as 

 cholera, diphtheria, typhoid, tuberculosis, and others, and 

 from the knowledge thus gained plan new and efficient 

 methods for combating and preventing disease. This new 

 field of study has not yet been by any means perfectly 

 explored. In so young a science, it is inevitable that much 

 must be accepted provisionally, and with the reservation 

 that it is more likely to be corrected by later knowledge 

 than are the facts of the older sciences. In many cases it 

 is difficult to avoid being drawn into generalizing the 



