140 The Microscope. 



various infective diseases of man and the lower animals. The 

 organs must first be hardened by one of the numerous harden- 

 ing processes, of which the one I generally adopt myself is to 

 place the organ, or a selected portion of it, for forty-eight hours 

 in dilute methylated spirit (1-2), and then transfer it to pure 

 methylated spirit, in which it may be kept for an indefinite 

 time. When it is sufficiently hardened, sections must be made 

 by hand, or with one of the microtomes. For photographic 

 purposes the sections should be cut as thin as possible, for 

 with thick sections a fogged picture will result. A perfect sec- 

 tion, but one rarely met with, would be one which is of the 

 thickness of a single cell throughout. 



To stain the sections, they are placed in the saturated wa- 

 tery solution of vesuvine or Bismarck brown, and allowed to 

 remain there about an hour, then washed with distilled water, 

 and afterwards in a half to one per cent, solution of acetic acid, 

 dehydrated in absolute alcohol, clarified in oil of cloves, and 

 mounted, with Canada balsam in xylol. The bacteria should 

 appear as deeply stained bodies standing out in bold contrast 

 with the diffusely and more lightly stained tissue elements. 

 The specimen should be covered with an extra thin cover-glass 

 (.004-005), for, if a thicker cover-glass is employed, a high- 

 power objective may not be capable of working through it. 

 The thickness of the cover glass can be easily gauged by El- 

 liott's gauging machine. 



The staining of bacteria, whether on the cover-glass or in 

 sections, will be found, with a little care and practice, perfectly 

 easy. The only difficulty is to hit off a mean between under- 

 staining and overstaining, so that the bacteria are neither too. 

 faintly nor too deeply stained ; but this is easily overcome — 

 Photographic Hews. 



"Dr. Stowell's journal is always a welcome guest. The 

 journal has steadily increased in value with time. I trust that 

 every well regulated knight of the tube feels as I do — that it 

 would be very poor economy indeed to do without this jour- 

 nal.— J. O. Stillson, M. D. 



