LABORATORY RESEARCH, ETC. 263 
colour is made lighter by washing with absolute 
alcohol and oil of ‘cloves, and the preparation is after- 
wards mounted in balsam. The nuclei of the cells are 
then of a carmine red, and the bacteria are violet; the 
rest of the preparation is of a much paler colour. 
Ehrlich’s Method—We mentioned this method 
when speaking of the bacillus of tuberculosis. It 
consists in treating the sections or mounted prepara- 
tion with a solution of methyl-violet in aniline oil, and’ 
the colour is afterwards quickly discharged in nitric 
acid; the bacteria alone remain violet. Fuchsin, 
methylene blue, coccinine, vesuvine, etc., are also em- 
ployed in various processes for staining bacteria. 
Measurement, Drawings, and Photographs.—Bac- 
teria are measured by comparing them with the 
divisions of the micro-millimetre slide placed on the 
stage of the microscope over the preparation. The 
microbes may be drawn without much difficulty by 
means of the camera lucida—at least, after a little 
practice, as their forms are not at all complex. But 
the results afforded by photography are, as it is plain, 
very superior, The photographic plate is indeed more 
sensitive than the eye, and often allows us to see 
details which had escaped the latter. Koch has given 
good illustrations of pathogenic bacteria in his book 
entitled, Beitrdge zur Biologie der Pflanzen, vol. ii. 
(1877). 
Methods of Microbe Cultwre.—The development of 
microbes may be observed by placing the drop of 
