PRACTICAL BACTERIOLOGY. 



firmly on to the layer of gum on the cork, which 

 is then placed iu absolute alcohol, in order to remove 

 the water from the gum. This generally takes 

 place in about five hours. Fish-glue is not to be 

 recommended, as most of the preparations sold under 

 that name are soluble in alcohol, and thus the 

 piece of tissue falls off. After the water has been 

 abstracted from the gum, the tissue is quite firmly 

 attached to the cork, which can now be screwed 

 tightly into the clamp of the microtome. The surface 

 of the tissue to be cut, as well as the edge of the knife, 

 are moistened with absolute alcohol, and sections of 

 from "02 to "06 mm. iu thickness are made. The 

 thinner the sections, the more easily, as a rule, are the 

 bacteria rendered visible. A convenient form of mi- 

 crotome is shown in Fig. 7. A minute description of 

 these instruments would be out of place here. 



The thin sections are now taken up with a needle 

 and a brush and put into absolute alcohol, from which 

 they are conveyed direct into the staining solution. 

 If typhoid bacilli are to be examined, the ordinary 

 aqueous solutions must not be used, as they have 

 not suflBcieat staining power for these organisms. A ' 

 staining solution must be prepared of 100 com. of 

 caustic potash solution (1 : 1000) and 30 ccm. of a 

 concentrated alcoholic solution of methylene blue 

 (Loffler's methylene blue). This fluid has much 

 stronger staining properties than the ordinary aque- 



