300 BACTERIOLOGY 



could not obtain any positive results with fungus spores 

 which were of a deep colour, or dull yellow- brown, although 

 ■colourless and faintly tinged spores were readily killed ; and 

 Bachmann found that in the spectra of 42 pigments of 

 fungi the extreme blue-violet (i.e. the most active part) is 

 •cut out from the line G on in all but two. 



Further, the sporangia and spores of ferns are mostly 

 orange or reddish, pollen and its spores, which contain oils, 

 are almost always deep orange, and lastly Ward suggests 

 that one of the functions of chlorophyll may be to act as a 

 •colour-screen. 



This observer therefore puts forth the provisional hy- 

 pothesis that : — ' No plant exposes a reserve store of fatty 

 material to the danger of prolonged or intense insolation 

 without a protective colour screen calculated to cut out at 

 least the blue-violet rays, as these rays would otherwise 

 destroy the reserve substance by promoting its rapid 

 ■oxidation.' 



D. Additio7ial Methods and Formidce 



Fixings methods. — For fixing coccidia, Flemming's solu- 

 tion, corrosive sublimate, or absolute alcohol may be used. 

 The last-named was dealt with on p. 80. 



By Flemming's method pieces of perfectly fresh tissue are 

 immersed in a mixture of 4 parts of 2 per cent, aqueous 

 solution of osmic acid, 15 parts of 1 per cent, chromic acid, 

 and 1 part of glacial acetic acid, for from one to three days, 

 washed in water for three to six hours, and then finally 

 hardened by successive immersion for twenty-four hours 

 each in 80, 60, and 96 per cent, alcohol. This method 

 gives great sharpness of definition, but the sections do not 

 stain readily. 



By the second method the fresh pieces are immersed for 

 six to twenty-four hours in a solution of 7^ grms. corrosive 



