82 A MANUAL OF BACTERIOLOGY 



For this purpose 1 grm. of faeces is thoroughly emulsified 

 in 10 c.c. of physiological salt solution, and 1 c.c. of the 

 suspension is introduced into the fermentation tube, the 

 long arm of which is 95 mm. long. The media employed 

 are 1 per cent, dextrose, lactose, and saccharose broths 

 made with " Lemco " (as above) or with sugar -free meat 

 broth (see p. 32). With such tubes normal stools yield 

 the following amounts of gas : x 



Dextrose. Lactose. Saccharose. 



26-75 . . . 29-9 . . . 19'5 mm. 



The Cultivation and Isolation of Micro-organisms 



It should be clearly understood that micro-organisms 

 cannot usually be identified by their microscopical cha- 

 racters alone. We can state from a microscopical exami- 

 nation the form of an organism, that it is a bacillus or a 

 micrococcus, or a sarcina, its size, that it is motile or non- 

 motile, sporing or non-sporing, but we cannot as a rule 

 go beyond this. It is necessary in most cases to ascertain 

 the characters of the growths of organisms on the various 

 culture media before species can be identified, and this is 

 the principal reason for having a varied assortment of 

 nutrient media. It is likewise necessary for the successful 

 cultivation of pathogenic organisms, i.e. those connected 

 with disease processes and developing in or upon the 

 bodies of man and of animals, to maintain the cultures 

 at a temperature approximating to that of the host. For 

 this purpose some form of incubator is required. This 

 consists of a box or chamber of copper or iron with 

 double walls (Fig. 13), the space between which is filled 

 with water, the outside being covered with wood or felt, 

 or some other non-conductor. The water between the 



1 See Herter and Kendall, Studies from the Rockefeller Institute (Reprints) 

 x, 1910. 



