CHAPTER IV. 



PREPARATION OP CULTURE-MEDIA FOR INOCULATION. 



WE have on a former page described the methods to obtain 

 eterile stock of nourishing media suitable for artificial cul- 

 tivations. The solids, as serum gelatine, serum, and hydro- 

 cele fluid, must, before solidification, be placed in test-tubes 

 and small flasks, and then sterilised in the manner above 

 described, to be made ready for establishing cultures, i.e. for 

 inoculation. The Agar-Agar mixture however can, like 

 broth, peptone mixture, beef extract solution, and gelatine 

 mixtures, be kept as stock in large flasks. When thus sterile, 

 these latter can be decanted into a number of test-tubes or 

 small flasks, in which the cultivation is to be carried out, 

 Gelatine mixtures (gelatine and broth, gelatine and peptone, 

 gelatine and beef extract) and the Agar-Agar mixture, must 

 of course be liquefied over a flame before being ready for 

 decanting. The test-tubes most suitable are about six inches 

 long, and should not be less than about one inch broad ; the 

 flasks are about of the capacity of one to two ounces, and 

 ought to have a neck of comparatively good width. The test- 

 tubes receive the fluids for about one and a half to two and 

 a half inches in depth, the flasks for about one-fourth to one- 

 third of their bulk. All these test-tubes and flasks with 

 their cotton-wool plugs, before receiving the material, should 

 be thoroughly sterilised by overheating. As I mentioned in 

 the previous chapter, this ought to be well borne in mind, for 

 starting with a sterile nourishing fluid i.e. one that has been 

 kept in the stock flask for several days to several weeks in 

 the incubator at a temperature of from 32 38 C. and that 

 has remained perfectly clear and limpid and working with 

 thoroughly sterilised test-tubes and cotton-wool plugs very 



