136 BACTERIOLOGY. 



Dormal outline of the cells is altered. If carefully dried 

 before fixing, this does not occur and the morphology 

 of the organism remains unchanged. A better plan for 

 the process of fixing is to employ a copper plate of 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 ar- 

 rangement one can get a graduated temperature, begin- 

 ning at the point of the plate above the gas-flame where 

 it is hottest, and becoming gradually cooler toward the 

 other end of the plate, which may be of a very low tem- 

 perature. By dropping water upon the plate, beginning 

 at the hottest point and proceeding 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 minutes, 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 preferred 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 sometimes occur from the too great 

 and irregular application of high temperatures may in 

 part be eliminated, or if not, will be more nearly con- 

 stant. The fixing consists in drying or coagulating the 

 gelatinous envelope surrounding 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 be- 

 ginner will have to deal stain readily with solutions of 

 any of the basic aniline dyes. 





