1 66 Methods of Observing Micro-organisms 



I lOO parts 



n. '..'.'.. 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. 



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 

 fiUed with distilled water. The red corpuscles at once begin to 

 hemolyze and the process is carried on to completion. When aU 

 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 magni- 

 fication and the method of manipulating the instruments must be 

 learned from dealers' catalogues. 



Photographing Micro-organisms. — This requires special apparatus 

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



* "Lancet," Jan. 10, 1903. 



t See the excellent chapter upon Photomicrography in Aschoff and Gaylord's 

 "Pathological Histology," Philadelphia, 1900. 



