414 DOURINE 



particular affinity for chromatin. Unless this polychromatophylic 

 change takes place the solution is useless. 



STOCK SOLUTION NO. 2. 



Eosin I part 



Water looo parts 



For staining, the stock solutions are separately diluted with water, 

 5 parts of stock solution to lOO parts of water. 



In order to obtain a smear, prick the center of the plaque and take 

 a drop of blood on a slide, which should be chemically clean, having 

 been taken from an alcohol bottle and dried with a clean piece of art 

 muslin. Then, either in the ordinary way with a piece of cigarette 

 paper, make a thin even smear over the slide, or, as an easier and 

 equally efficient method, take a perfectly clean flat large-sized needle 

 and place it edgeways on the drop, when the capillary attraction of the 

 needle will cause the blood to stream right across the slide ; then 

 evenly and gently draw the needle down the length of the slide, and a 

 very even smear may be obtained. Quickly dry the smear in the air by 

 waving rapidly about, which prevents the red corpuscles from crenat- 

 ing ; the slide can then be kept indefinitely or used at once. The 

 advantages of using a slide instead of a cover-glass are that you get a 

 much larger field on which to work, it is much more easily manipulated 

 and it can be kept without any mounting. Place the film in absolute 

 alcohol or alcohol and ether, for fifteen minutes to half an hour, to 

 fix. This coagulates the albumen and makes a permanent film in which 

 the corpuscles and organisms are retained. Remove from the alcohol, 

 wash in water, and then apply the stain. This is made by mixing equal 

 parts of the above two solutions, freshly prepared, in a small glass 

 measure or porcelain dish. It is important that the admixture should 

 be as fresh as possible. Apply the stain to the whole of the film and let 

 it remain for seven to ten minntes ; wash in water and dry in the air, 

 no heat being applied. The red corpuscles may have a bluish tinge, 

 which may be removed by further washing. If the blood platelets 

 appear bluish the film requires further staining ; they should appear as 

 ruby-red granular bodies. By continuous application of water the stain 

 may be washed out, but the film may always be stained over again. 



By this stain the protoplasm of the trypanosome is stained blue, the 

 nuclear chromatin a carmine violet, and the flagellum and centrosome a 

 brilliant red. The red corpuscles will be a pinkish colour, and the vari- 

 ous forms of leucocytes will be well differentiated. In examining the 

 smear, time may be saved by looking along the edge of the film, as it is 

 here that the parasites will be most numerous if they are present, as 

 they, being like the leucocytes of less density than the rest of the blood, 

 tend to run to the periphery when the smear is made. 



A film made in this way requires no cover-glass, but if the cedar oil 



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