142 



BAOTERIOLOGY. 



SO that the tissue may be brought closer to or farther 

 from the plane in which the knife slides. By this 

 arrangement sections of any desired thickness can be cut 

 by turning the milled disc with the one hand and causing 

 the knife to traverse the tissue with the other. 



The tissue and the knife-blade should be kept wet 

 with alcohol, so that the sections may float upon the 

 blade of the knife, from which they can be easily 

 removed without tearing, with a curved needle or a 

 camel-hair pencil. As the sections are cut they are 

 placed in a dish containing alcohol. 



Fig. 22. 



There are some tissues which, by reason of their his- 

 tological structure, do not become sufficiently dense when 

 exposed to alcohol to permit of their being cut in the 

 above way. It becomes necessary to render them more 

 solid by filling their interstices with some substance that 



