Staining Protozoa in Tissue 169 



1 100 parts 



II 20 " 



III SO " 



At the time of staining dilute the mixture i : 60 or i : 100 with water. 

 To test the solution: (i) Acetic acid makes it redder. (2) A drop of 

 the solution on filter-paper should make a blue spot with a green 

 center and an orange border. If a red zone appears outside of the 

 orange, too much acid fuchsin is present. 



1. Stain the sections from six to twenty-four hours. 



2. Wash out a little in 90 per cent, alcohol. 



3. Dehydrate in absolute alcohol. 



4. Xylol. 



5. Xylol balsam. 



It is important to place the sections directly from the staining fluid into the 

 alcohol, because water instantly washes out the methyl-green. 



Measurement of Micro-organisms. — They can best be measured 

 by an eyepiece micrometer. As these instruments vary somewhat 

 in construction, the unit of measurement for each objective magni- 

 fication and the method of manipulating the instruments must be 

 learned from the dealers' catalogues. 



Photographing Micro-organisms. — ^This requires special apparatus 

 and methods, for which it is necessary to refer to special text-books.* 



* See the excellent chapter upon Photomicrography in Aschoff and Gaylord's 

 "Pathological Histology," Philadelphia, igoo. 



