2 A MANUAL OF BACTERIOLOGY 



mode of growth, multiplication, and the products it 

 may give rise to. In fact, Dr. E. Koch l has laid 

 down the following canons _to ascertain whether a 

 microbe is, directly or indirectly, the causa causans 

 of a particular disease: 



(1.) The microbe in question must have been 

 found either in the blood, lymph, or tissues of the 

 man or animal which is suffering from, or who has 

 died of, the disease. 



(2.) The microbe taken from this medium (blood, 

 tissues, etc.), and artifically cultivated in certain 

 media, 'must be transferred from culture to culture 

 for several successive generations, taking the pre- 

 cautions necessary to prevent the introduction of 

 any other microbe into these cultures, so as to 

 obtain the specific microbe, pure from every kind of 

 matter proceeding from the body of the animal 

 whence it originally came. 



(3.) The microbe, thus purified by successive cul- 

 tures, and reintroduced into the body of a healthy 

 animal capable of taking the disease, ought to re- 

 produce the disease, in the animal, with its char- 

 acteristic 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 medium. 



Microbes are everywhere present in the air, in 

 the earth, and in waters ; in and on food, clothes, 

 etc. ; consequently they gain admittance into the 

 bodies of man and animals. These microbes do not 



1 Die Milzbrand-impfung, 1883. 



