Microscopic Study of Cultures 259 



amination of it with any power beyond that given by a 

 hand -lens. 



MICROSCOPIC STUDY OF CULTURES. 



Some attention has been given to the preparation of micro- 

 tome sections of the gelatin growth, which can be done if the 

 glass be warmed just sufficiently to permit the gelatin con- 

 taining the growth to be removed and placed in Miiller's 

 fluid (bichromate of potassium 2-2.5, sulphate of sodium i, 

 water 100), where it is hardened. When quite firm it is 

 washed in water, passed through alcohols ascending in 

 strength from 50 to 100 per cent., embedded in celloidin, cut 

 wet, and stained like a section of tissue. 



A ready method of doing this has been suggested by 

 Winkler,* who bores a hole in a block of paraffin with the 

 smallest size cork-borer, soaks the block in bichlorid solution 

 for an hour, pours liquid gelatin into the cavity, allows it to 

 solidify, inoculates it by the customary puncture of the 

 platinum wire, allows it to develop sufficiently, and when 

 ready cuts the sections under alcohol, subsequently staining 

 them with much diluted carbol-fuchsin. 



Neat museum specimens of plate and puncture cultures 

 in gelatin can be made by simultaneously killing the micro- 

 organisms and permanently fixing the gelatin with formal- 

 dehyd, which can either be sprayed upon the gelatin or ap- 

 plied in dilute solution. As gelatin fixed in formaldehyd 

 cannot subsequently be liquefied, such preparations will last 

 indefinitely. 



Standardizing Freshly Isolated Cultures. This is a 

 matter of some importance, as in bringing bacteria into 

 the new environment of artificial cultivation their bio- 

 logic peculiarities are temporarily altered, and it takes 

 some time for them to recover themselves. While the 

 appearances of the freshly isolated organism should be 

 carefully noted, too much stress should not be laid upon 

 them, and before beginning the systematic study of any 

 new organism it should be made to grow for several suc- 

 cessive generations upon two or three of the most impor- 

 tant culture media. Its saprophytic existence being thus 

 established, the characteristics manifested become the per- 

 manent peculiarities of the species. 



* " Fortschritte der Medicin," Bd. xi, 1893, No. 22. 



