200 Methods of Observing Micro-organisms 



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 washes out the methyl-green 

 instantly. 



Ross' Thick Blood-spreads. In case the number of parasites in the 

 blood is very small, so that they would be scattered sparingly 

 over a large area of the ordinary blood spread, Ross* has suggested 

 a modification of the technic by which they can be more readily 

 found. To do this a very thick spread is prepared and dried. 

 As soon as it is dry, and without fixing, the slide is stood vertically 

 in a vessel filled with distilled water. The red corpuscles at 

 once begin to hemolyze and the process is carried on to com- 

 pletion. When all of the hemoglobin has been removed, the 

 slide is taken out, dried, and then fixed and stained. There 

 now being no red corpuscles to distract the attention or obscure 

 the vision, the stained parasites can quickly be found. 



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 magnification and the method of manipu- 

 lating the instruments must be learned from dealers' cata- 

 logues. 



Photographing Microorganisms. This requires special 

 apparatus and methods, for which it is necessary to refer 

 to special text-books. f 



* "Lancet," Jan. 10, 1903. 



f See the excellent chapter upon Photomicrography in Aschoff and 

 Gaylord's "Pathological Histology," Philadelphia, 1900. 



