160 BACTERIOLOGY. 



different reactions, are to be studied. The property of 

 producing fermenta,tion with the liberation of gases 

 must be ascertained ; if it produces pigment, what are 

 the conditions favorable and unfavorable to this func- 

 tion ; and lastly, we must consider its behavior when 

 introduced into the bodies of animals used for experi- 

 mental work — i. e., is it a disease-producing organism, 

 or does it belong to the group of innocent saprophytes ? 

 We have learned the methods of obtaining colonies, 

 and have acquainted ourselves with some of the pecu- 

 liarities by which they are distinguished from one 

 another. The next important step is to determine the 

 morphology of the individuals composing these colo- 

 nies as well as their relation to each other in the colony. 

 These points are decided by microscopic examination 

 of bits of the colony which are transferred to thin 

 glass cover-slips, upon which they are dried, stained, 

 and mounted. Cover-slips for this purpose are pre- 

 pared in two ways : either by taking up a bit of the 

 colony on a platinum needle, smearing it upon a cover- 

 slip, staining it, and examining it^ — by which only the 

 morphology of the individuals can be made out — or by 

 the method of " impression cover-slip preparations," 

 by which not only the morphology, but also the relation 

 of the organisms to one another in the colony can be 

 determined. The details of these methods will be 

 found in the chapter on the methods of staining. 



miceoscopic examinatiohr of peepaeations. 



The Different Parts of the Microscope. — 

 Before describing the process of examining prepara- 

 tions microscopically, a few definitions of the terms 



