SCHIZOMYCETES AND SACCHAROMYCETES 295 



investigation, in face of the contention that in men and 

 animals, and probably plants, they are the associates, and in 

 many cases the causes, of disease. Since = fi 



the discovery of the Bacillus of anthrax, 

 or splenic fever (Fig. 136), facts have 

 rapidly developed in the association of 

 microbes with contagious diseases, which 

 previously were theoretically attributed to 

 many sources. That which at first was c^g' 

 an hypothesis is now an ascertained FiG _ m __ Ba< ,,, NS „„. 

 fact ; but before an infectious disease can thratis. Chatto and 

 be considered due to the presence of a m M- 

 specific microbe, it must submit to the test of the four 

 rules established by Koch. (1) " The microbe in question 

 must have been found either in the blood or tissues of the 

 man or animal which has died of the disease. (2) The 

 microbe taken from this medium, and artificially cultivated 

 out of the animal's body, must be transferred from culture to 

 culture, for several successive generations, taking the precautions 

 necessary to prevent the introduction of any other microbe 

 ^_^ ===== — = — s ^ = ^.. into these cultures, 



" ^= ^ = "~ so as to obtain the 



specific microbe, pure 

 from every kind of 

 matter proceeding 



Fiq. 137. — Development of the Bacillus anthracis. from the bodv of the 

 After Bwart. J 



animal whence it 

 originally came. (3) The microbe thus purified by successive 

 cultures, and reintroduced into the body of a healthy animal, 

 capable of taking the disease, ought to reproduce the disease 

 in question in that animal, with its characteristic symptoms 

 and lesions. (4) Finally, it must be ascertained that the 

 microbe in question has multiplied in the system of the 

 animal thus inoculated, and that it exists in greater number 

 than in the inoculating liquid." These conditions have been 

 fulfilled in the case of a large number of diseases, such as 

 anthrax, swine-fever, smallpox, erysipelas, etc., and the microbe 

 theory of the origin of contagious diseases is, in principle, 

 accepted as fact. 



