CHAPTER IV. 



COLLECTION OF MATERIAL FOR BACTERIOLOGICAL 



STUDY. 



Bacteria under natural conditions are usually associated as 

 mixtures of several species living together. Only under rather 

 exceptional circumstances will a single kind of bacteria be found 

 growing alone. This does occur in disease, however, where the 

 living host may be able to keep out all but the one kind of mi- 

 crobe. But even diseased tissues or exudates originally harbor- 

 ing only one kind of bacteria may quickly acquire others in abun- 

 dance after removal from the living body. It is well therefore 

 to regard any material presented for bacteriological examination 

 as potentially, and in all probability actually, harboring several 

 kinds or species of bacteria. The direct planting of such material 

 on a culture medium .will, therefore, in most instances give rise 

 to a mixed culture, in which those forms least prominent in the 

 original material may easily appear as most important. If the 

 material be allowed to stand, especially if it be a favorable 

 medium for bacterial growth, the relationships present may be- 

 come seriously confused. It should, therefore, be examined as 

 fresh as possible. When immediate examination is impossible 

 the material should be kept on ice. 



Samples of water, milk or other fluid should be collected in 

 sterilized tubes or bottles. Samples of solid food should be 

 seared or charred all over the surface and divided with a sterilized 

 knife. A small piece of the interior is then removed to a sterilized 

 glass dish and covered. 



Material removed from the human or from the animal body dur- 

 ing life or at autopsy may.be, bacteria-free, : or it may contain 

 one or more specie^, of -microbes. Ijt is irnportaiit that the picture 



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