OF THE HUMAN SUBJECT. 25 



ments of a chain or streptococcus elongated in the direction of 

 its length, i.e., oval in place of spherical. 



The microscopical examination of bacterial cultures may be 

 reduced to a comparatively simple technique. Bacteria may be 

 examined after being dried, or in their natural condition. The 

 advantage of the first method is that the preparations are perma- 

 nent, and to this must be added the greater facility with which 

 they admit of being drawn or photographed. Under the other, 

 the organisms suffer no reduction in size or alteration in form, 

 nor can appearances artificially produced be mistaken for such as 

 are natural. There is the same difference, in short, as between 

 the study of plants growing in a garden and those dried in a 

 herbarium. The second method is, therefore, in all cases pref- 

 erable; obviously for the study of growth and reproduction it is 

 absolutely necessary. 



The Hanging Drop. Examinations in the natural state are 

 carried out by means of the hanging drop, which may be de- 

 scribed in detail as being the most beautiful of all methods, and 

 as expeditious as any. 



If a culture on agar or gelatine (when this is not liquefied 

 by the growth) is to be examined, a thin, narrow ring of vaseline 

 is painted around, but a short way from the depression of a hol- 

 low ground slide; a single 6'se or loop of distilled water is then 

 transferred to the centre of a square or circular cover-glass (No. 

 1 thickness). For the sake of those unacquainted with such 

 matters, it may be said that the 6'se or loop is a small eyelet 

 made at one end of a piece of platinum wire about two and a 

 half inches in length, the other end of which is pressed into the 

 end of a piece of solid glass rod, seven inches long, softened in the 

 flame of a Bunsen burner; the diameter of the eyelet, which is 



