142 nAOTERIOLOOY. 



altered. If carefully dried before fixing, this does not 

 occur and the morphology of the organism remains un- 

 changed. A better plan for the process of fixing is to 

 employ a copper plate about 35 cm. long by 10 cm. 

 wide by 0.3 cm. thick. This plate is laid upon an iron 

 tripod and a small gas-flame is placed beneath one of 

 its extremities. By this arrangement one can get a 

 graduated temperature, beginning at the point of the 

 plate above the gas-flame where it is hottest, and becom- 

 ing gradually cooler toward the other end of the plate, 

 which may be of a very low 'teniperature. By dropping 

 water upon the plate, beginning at the hottest point and 

 proceedi tig: toward the cooler end, it is easy to determine 

 the point at which the water just boils; it is at a little 

 below this point that the cover-slips are to be placed, 

 bacteria side up, and allowed to remain about ten min- 

 utes, when the fixing will be complete. The same may 

 be accomplished in a small copper drying-oven, which 

 is regulated to remain at the temperature of 95° to 

 98° C. In very particular work this plan is to be pre- 

 ferred to the process of passing the cover-slips through 

 the flame, as the organisms are always subjected to the 

 same degree of heat, and the distortions which some- 

 times occur from the too great and irregular application 

 of high temperatures may in part be eliminated, or, if 

 not, will be more nearly constant. The fixing consists 

 in drying or coagulating the gelatinous envelope sur- 

 rounding the organisms, by which means they are caused 

 to adhere to the surface of the cover-slip. When 

 fixed, the staining is usually a simple matter. The 

 majority of bacteria with which the beginner will have 

 to deal stain readily with solutions of any of the basic 

 aniline dyes. 



