DIFFERENT PARTS OF THE MICROSCOPE. 199 



to be studied. The property of producing fermentation 

 with the liberation of gases, and the character and quan- 

 titative relations of tliese gases, must be ascertained. If 

 it produces pigment, what are the conditions favorable 

 and unfavorable to this function. And, lastly, we must 

 consider its behavior when introduced into the bodies 

 of animals used for experimental 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 steps are to determine the 

 moi'phology of the individuals composing these colonies, 

 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 prepared 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 individual bacteria 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 in the colony to one another can be deter- 

 mined. The details of these methods will be found in 

 the chapter on the Methods of Staining. 



microscopic examination of preparations. 



The Different Parts op the Microscope. — 

 Before describing the method of examining prepara- 

 tions microscopically, a few definitions of the terms 



