CHAPTER V 



ARTIFICIAL INFECTION 



Infection experiments, or, as usually termed, artificial infection 

 experiments, are essential in pathological work. They may be 

 undertaken for a variety of purposes, among which the most 

 important seem to be the following : 



i. To determine if a given organism is parasitic, or the cause 

 of a particular disease. 



2. To determine the conditions under which an organism is 

 most active in producing a disease, as well as the natural seat 

 and manner of infection. 



3. To determine the range of pathogenicity of a given organism ; 

 that is, to demonstrate what varieties, species, genera, etc., may be 

 considered, potentially at least, host plants. 



4. To determine the relationship of the different stages of an 

 organism to one another and to the host, or hosts. 



5 . To determine the conditions under which the different stages 

 of a fungus may be developed. 



6. To determine the special relation of a parasitic organism to 

 lesions or abnormalities of the host, with which a parasitic organism 

 may be constantly associated. 



The rules of proof formulated by Koch, especially for disease- 

 producing bacteria, have been repeatedly brought before investi- 

 gators, yet they are too frequently ignored. They are appropriately 

 termed the canons of Koch. They should be kept in mind in all 

 pathological work, as they are applicable in all such studies, despite 

 the exceptions which may sometimes be made. These rules may 

 be expressed as follows : 



a. Under diverse conditions the fungus must be constantly and 

 abundantly associated with the disease, or pathological state. 



b. The organism should be grown in pure cultures, when pos- 

 sible, and its differential characteristics well studied. 



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