204 THE EXAMINATION OF MATERIAL 



A warm stage can be used to maintain the preparations at the temperature of the 

 body (p. 135). 



(b) Scrapings of organs. Scrapings of the internal organs are to be 

 collected in the manner already described (Chap. XL), and transferred with 

 a platinum loop to a slide on which they are rubbed up in a drop of filtered 

 water or, better, in a drop of normal saline solution (water 1000, NaCl 8, 

 filter, distribute in tubes, sterilize in the autoclave) ; then spread the material 

 with a platinum loop, cover with a cover-glass, and examine at once 

 (obj. D ; oc. 2 Zeiss). 



2. Stained preparations. 



Before being stained fluids and scrapings of organs should be spread in a 

 thin layer on a slide or cover-glass, and dried and fixed to preserve the form 

 of the cells and to make them adhere to the surface of the glass. 



A. Preparation of films. 



(a) Fluids. 



The treatment of fluids such as blood, serous exudates, pus, etc., will first 

 be described. 



1. Spreading of films, (a) On cover-glasses. 1. Hold a perfectly clean 

 cover-glass by one of its angles, A, and place a drop of the fluid to be 

 examined in the centre. 



2. Cover with a second cover-glass laying the latter 

 across the former as shown in the figure (fig. 151). 



3. Take hold of the second cover-glass at the angle 

 \ B B, opposite to A, and slide them apart so that the 

 * liquid is spread out in a thin, uniform layer. 



4. Allow the films to dry either in the air or by 

 placing them on a drying stand heated to 40 or 45 C. 

 (fig. 127, p. 141). 



(/3) On slides. For pus, serous exudates, etc., slides 

 may be used in a similar way to cover-glasses : place 

 the drop of fluid near one end of the slide, lay another slide over it and 

 then draw the two slides apart. 



For blood the following method is better : 



1. Take a perfectly clean slide and lightly touch the drop of blood as it 

 oozes from the prick, taking care that the blood is drawn up by the slide 

 and not the slide pressed down on to the drop. 



2. Hold the slide in the left hand, apply the edge of a cover-glass to the 

 drop of blood and the latter will spread along the edge of the cover-glass by 

 capillary action. (The end of a slide or a visiting card or even a small glass 

 stirring rod will serve equally as well as a cover-glass.) 





FIG. 152. Preparation of a blood film on a slide. 



3. Draw the cover-glass slowly and without pressing upon it towards the 

 other end of the slide. In this way a very thin and uniform layer of blood 

 is left on the slide which dries as fast as the cover-glass passes over it (fig. 152). 



The preparation of satisfactory blood-films requires a certain amount of practice, 

 so that if the first attempts fail one must not be discouraged ; remember always 

 that absolutely clean and flat slides and cover-glasses are indispensable. 



