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fIDicro6copical C^ecbnique, 



Preservation of Structures by Formalin*— Hauser refers to 

 his former experiments, in which it was shown that cultures could 

 be preserved by means of formalin vapour. Gegner proved that 

 gelatin exposed for a long time to formalin vapour does not 

 become fluid at the body heat. The author further shows that at 

 no temperature can it be liquefied. At the same time, the gelatin 

 is in this way permanently sterilised and remains unchanged. 

 Thus, formalin is a most useful means of preserving cultures, the 

 only condition being that they should not be allowed to dry up. 

 It is also specially adapted for microscopic culture preparations. 

 After thus fixing the gelatin in not too thick a layer, the part which 

 it is desired to keep should be detached with a sharp spatula. 

 This is put on a slide with gelatin of similar composition, and a 

 cover-glass applied. The preparation is then put into the formalin 

 vapour chamber for twenty-four hours. Lac is applied round the 

 cover-glass to prevent drying. Cultures can also be made on 

 slides in the first instance. The author has tried these methods 

 with success in the case of many micro-organisms. The culture 

 can also be stained by a weak, watery fuchsin solution. Another 

 method is to let the coloured gelatin culture dry upon the slide, 

 and then mount in Canada balsam. The colony should in all 

 cases lie in the centre of the gelatin. 



Bleaching Vegetable Sections.t— Coles' method of preparing 

 sections for staining is to bleach by means of a solution of chlorin- 

 ated soda, the length of time varying according to the condition 

 and nature of the tissues. Wash several times in fresh water, and 

 finally with water containing eight or ten drops of nitric acid to 

 each half-pint. Transfer sections to alcohol for an hour before 

 staining. 



Oil of Cassia as a Medium.— Oil of cassia has a higher refrac- 

 tive index than cedar oil, and Dr. H. G. Piffard finds it brings 



* Munch. Med. Woch.^ Aug. 29, 1893, i^ Brit. Med. Journal, Nov. 4, 1893. 

 t Methods of Microscopical Research. 



