MICROSCOPIC EXAMINATIONS. 105 



tion of gases must be ascertained ; 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 for obtaining colonies, 

 and have studied some of the peculiarities which are to 

 distinguish them from one another. The next important 

 step is to determine the morphology of the individuals 

 composing these colonies as well as their relation to each 

 other in the colony. These points are decided by micro- 

 scopic examination of bits of the colony which have been 

 transferred to thin glass cover-slips, upon which they are 

 dried, stained, and mounted. Cover-slips for this pur- 

 pose are prepared in two ways : either by taking up a 

 bit of the colony on a 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 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 of the Microscope.— 

 Before describing the process of examining preparations 

 microscopically, a few definitions of the terms used in 

 referring to the microscope may not be out of place. 



The ocular or eye-pieoe is the lens at which the eye 

 is placed in looking through the instrument. 



The objective is the lens which is at the distal'end of 



