CHAPTER IV 



METHODS OF INVESTIGATING MICROBIAL DISEASES 

 THE INOCULATION AND DISSECTION OF ANIMALS- 

 HANGING -DROP CULTIVATION INTERLAMELLAR 

 FILMS THE MICROSCOPE 



THE systematic study of a condition dependent on the 

 activity of micro-organisms is in many instances no light 

 matter. When only one or two forms are present and 

 these are readily cultivated it may be comparatively 

 easy, but when there are many the investigation may 

 become exceedingly complicated. The first step to be 

 taken is to ascertain by careful microscopical examina- 

 tion the general characters of any organisms that may 

 be present in the material, and their distribution both 

 in the fresh condition and in stained preparations, and 

 if possible at different stages of the disease. In disease 

 conditions, for example, the blood and secretions may be 

 examined both before and after death, but in the latter 

 it must be remembered that soon after the fatal event 

 adventitious organisms rapidly make their appearance, 

 gaining access from the air and from the intestinal tract. 

 If organisms be detected an attempt should be made to 

 determine whether there is any predominant form and 

 if this is constantly present at different stages. If 

 organisms are found, it simplifies matters, but if not, it 

 cannot therefore be said that they are absent, for they 

 may be few in number, and consequently be missed in a 

 microscopical examination ; or they may be confined to 



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