CHAPTER VlTl 

 CULTURES, AND THEIR STUDY 



The purposes for which culture-media are prepared are numerous. 

 Through their aid it is possible to isolate the micro-organisms, to keep 

 them in healthy growth for considerable lengths of time, during 

 which their biologic peculiarities can be observed and their metaboUc 

 products collected, and to introduce them free from contamination 

 into the bodies of experiment animals. 



The isolation . of bacteria was next to impossible until the fluid 

 media of the early observers, were replaced by the solid culture-media 

 introduced by Koch, and exceedingly diflEicult until he devised the 

 well-known "plate cultures." 



A growth of artificially planted micro-organisms is called a culture. 

 If such a growth contains but one kind of organism, it is known as a 

 fure culture. 



It has t present become the custom to use the term "culture" 

 rather loosely, so that it does not always signify an artificially 

 planted growth of micro-organisms, but may signify a growth taking 

 place under natxiral conditions; thus, the typhoid bacillus is said to 

 occur in "pure culture" in the spleens of patients dead of typhoid 

 fever, because no other bacteria are associated with it; and some- 

 times, when the tubercle baciUi are very numerous and unmixed 

 with other bacteria, in the expectorated fragments of cheesy 

 matter from tuberculosis pulmonalis, they are said to occur in 

 "pure culture." 



The culture manipulations are performed either with a sterilized 

 platinum wire or with a capillary pipet of glass. 



The platinum wire is so limber that it is scarcely to be recom- 

 mended, and a wire composed pf platinum and iridium, which is 

 elastic in quaUty, is to be preferred. ■ The wires are about 5 cm. 

 i.' length, of variotis thickness according to the use for which they 

 are employed, and are usually fused into a thin glass rod about 

 17 cm. in length. The wires may be straight or provided with a 

 small loop at the end so as to conveniently take up small drops 

 of fluid. Heavy wires used for securing diseased tissue from ani- 

 mals may be flattened at the ends by hammering, and may thus 

 be fashioned into miniature knives, scrapers, harpoons, etc., as 

 desired. 



Ravenel has invented a convenient form for carrying in the pocket. 

 It consists of the platinum wire fastened in a heavier aluminium wire 

 which in turn fits into a piece of glass tubing. When carried in 



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