1894.] MICROSCOPICAL JOURNAL. 109 



fresh and 48-liour cultures of both diphtheria and anthrax 

 as tested by subcultures. 



Besides its use as here stated, I have used formalin to 

 sterilize instruments and hands, to" harden tissue and to 

 render gelatine insoluble. 



Gelatine, as is well known, melts at a comparatively 

 low temperature, but after 24 hours exposure to formalin 

 vapor it not only becomes insoluble in water, but loses its 

 property of becoming liquid at elevated temperatures. 

 Indeed I found by experiment that Schering's claim that 

 it would not become liquid even when placed in the flame 

 of the bunsen burner is true, the gelatine under these cir- 

 cumstances chars and may be burned but will not melt. 



In bacteriology formalin is thus very valuable for class 

 work for as pointed out by Hauser, quoted by Schering, 

 plates, stab and smear cultures can be prepared and 

 when the proper stage of development has been reached 

 the vapor disengaged at the room temperature from a 

 few drops of formalin will arrest further growth and 

 render the cultures harmless in case of breakage without 

 in any way altering their appearance. Colonies can also 

 be permanently mounted by putting them with a little 

 of the surrounding gelatine or agar on a slide, running 

 a little of the melted medium under the cover, exposing 

 this for 24 hours to formalin vapor and then spinning 

 around a ring of cement to prevent evaporation ; or, what 

 is better, as it prevents pressure from the cover, mount- 

 ing in a deep cell after sterilizing with formalin. 



For sterilizing instruments I have used a 10 per cent 

 solution in alcohol. This so far as I can see has no bad 

 effect upon the metal or cutting edge. For sterilizing my 

 hands I have used a J per cent to 1 per cent solution. It 

 is stated that formalin tans tissue and that when painted 

 in full strength over the skin, the tissue involved separ- 

 ates without suppuration after a few days, leaving a 

 rather deep eschar. I have accidentally spilled the pure 



