Fermentation and Kindred Phenomena. 103 



animal susceptible to the disease, and in this way to show that 

 the animal becomes affected with the same disease as the one 

 from which the organisms were originally derived. 



(4) It is necessary that in this so affected new animal the 

 same micro-organisms should again be found. u A particular 

 organism may be the cause of a particular disease, but, that 

 really and unmistakably it is so can only be inferred with 

 certainty when every one of the above conditions are fulfilled." 

 (Klein.) 



You will allow me to glance for a few moments at some of the 

 most important diseases which have been thus shown to be 

 intimately associated with micro-organisms. 



Tuberculosis. — This terrible disease, of which so many sufferers 

 die a lingering death, was proved by Koch to be due to a par- 

 ticular species of rod -like organism, which is called in consequence 

 bacillus tuberculosis. They are a great deal shorter and thinner 

 than the bacilli of spleen fever. Koch showed that they occur 

 in all tubercular growths of men, monkeys, cattle, birds, and 

 other animals, and in man they are found in the blood and 

 sputum. It is possible to cultivate them in an artificial nutrient 

 medium, best in solid blood serum ; and the disease can be 

 communicated to a healthy animal by injecting such a culture 

 into its system. In guinea-pigs and rabbits the disease requires 

 a period of "incubation" of three weeks and more ; that is to 

 say, this period intervenes between the time of inoculation and 

 the first symptoms of the disease. It has been shown by inhala- 

 tion and feeding experiments that animals can be inoculated ; 

 and as the bacilli themselves require a high temperature for 

 their development it is probable that the disease is spread either 

 by the inhalation of the spores or by their being swallowed 

 with the food. 



Cholera is one of the most dreaded of all diseases. Fearful 

 for the wholesale slaughter it causes when a locality is once, 

 so to speak, in its grasp, and fearful also for the terrible rapidity 

 of its action. It is said to originate in the valley of the Ganges, 

 where it is permanent or endemic, and yearly it spreads over 

 India. In Europe it first appeared at the commencement of 



