124 



THE AMERICAN MONTHLY 



[Jniy, 



on the turntable. Finishing cement 

 was then applied over the wax from 

 inner edge of cell down to and upon 

 the slide, and the mount was com- 

 plete. 



My own experience leads me to 

 conclude that the condemnation of 

 wax cells and the use of wax on ac- 

 count of the sweating so common 

 when it is used was premature. A wax 

 cell with a covering layer of cement, 

 if used when freshly made, will fre- 

 quently sweat, but if well seasoned 

 will scarcely ever sweat, according to 

 my experience. The wax appears to 

 soften some cements, probably be- 

 cause they contain some solvent of the 

 wax, and these will sweat no matter 

 how old, unless years be allowed for 

 seasonins: : hence cements containing 

 turpentine or oil should not be used 

 for covering wax cells, but benzole 

 being so volatile will wholly leave the 

 wax in a few weeks, hence, as well 

 as on account of its color, I generally 

 employ brunswick black. 



The cells made as advocated in the 

 article referred to have this advantage, 

 that the slide may be left (and freely 

 used) with no other cement than the 

 primary wax filling around the etlge 

 of cover for months or years until it 

 is seen whether any sweating will oc- 

 cur. If it does occur, by placing the 

 slide on a turntable the wax filling can 

 be instantly turned out with a sharp- 

 pointed knife-blade, the cover freed, 

 object removed, and cell recoated, or 

 the cover simply cleaned and replaced 

 as before in a minute or two, and thus 

 objects too hastily mounted may be 

 remounted or recovered with the least 

 loss of time, which cannot be done 

 so well or so quickly where covers 

 have been cemented down with any 

 of the cements ordinarily used. 



[There is one point in the above 

 communication to which we wish to 

 refer, as it is of considerable impor- 

 tance. In reference to the sweating 

 of the wax cells, w^hereby a deposit 

 forms on the under surface of the 

 cover-glass, which interferes with the 

 clearness of vision, the author seems 



to think such a deposit is not neces- 

 sarily an evil when wax cells are 

 used. For a long time, while many 

 different persons were relating their 

 experiences with wax cells a few 

 years ago, we w^ere of the same 

 opinion, which we regarded as fully 

 sustained by the excellent condition 

 of a large number of mounts of foi-am- 

 inifera, mounted dry in wax cells, 

 which were then sevei'al years old. 

 Since we have been in Washington, 

 however, a great change has taken 

 place in those slides, and the covers 

 are now quite generally coated with 

 the deposit complained of. It should 

 be remembered that in this case the 

 mounts remained in a perfect condi- 

 tion certainlv four or five years, and 

 then the change took place. Perhaps 

 the explanation may be found in the 

 climatic influences, but it scarcely 

 seems possible that the slight differ- 

 ence in the average temperature in 

 New York and Washington could 

 bring about such a result. — Ed.] 

 o 



A Few Simple Methods of Obtain- 

 ing Pnre Cultures of Bacteria for 

 Microscopical Examination.* 



BY DR. THEOBALD SMITH. 



The bacteria may be broadly di- 

 vided into two classes, the parasitic 

 and the saprophytic. Of course there 

 are numerous gradations between 

 these extremes. These remarks will 

 be confined more especially to the 

 methods of obtaining pure cultures 

 of the saprophytic bacteria. 



A convenient method of obtaining 

 pure cultures of a typical bacillus — 

 the so-called hay bacillus — is to take 

 some finely cut hay and make an in- 

 fusion of it. This is to be boiled for 

 from one-half to one hour in a flask, 

 plugged with cotton wool, and then 

 put into the incubator, or in fact in 

 any warm place. In the course of 

 two or three days a membrane will 

 appear upon the surface of the in- 

 fusion. Upon examination this mem- 

 brane will be fovmd to consist entirely 



' Abstract of a communication to the Washington 

 Microscopical Society, May 25, 1886. 



