746 THE ANIMAL PARASITES OF MAN 



is luted with vaseline or paraffin and examined first with a low power 

 and then with a high power objective. The light is cut down by 

 partly closing the diaphragm of the substage of the microscope. 



Skin Ulcers and Similar Sores. Scrapings are made from the edge 

 of the sore, mixed with sterile physiological salt solution, and 

 prepared and examined as above. 



Faces. A small portion of faeces, or flakes of mucus (which may 

 be blood-stained) from the same, is removed on a sterile platinum 

 loop, spread out thinly after dilution, if necessary, with physiological 

 salt solution on a slide, covered and examined as before. 



Alternatively, hanging drop preparations of blood, ulcerative tissue, 

 or faeces, appropriately diluted if necessary with sodium citrate or 

 physiological salt solution, may be made on a cover-slip, which is 

 inverted over a slide with a well in it. The cover-slip is then luted and 

 examined. 



For the elucidation of the developmental processes of such 

 organisms as trypanosomes, spirochaetes and piroplasms, fresh 

 preparations may be often kept under observation longer by the 

 use of a thermostat, maintained at or near blood heat, in which the 

 microscope is inserted. 



(b) Infra vitain Staining of fresh Preparations. 



Iniva vitain staining is of service on some occasions, more 

 particularly for the study of the nucleus and other chromatoid 

 substances of the living organism. Two methods are in common 

 use. In the first case, the stain, employed usually in very dilute 

 solution, is mixed with the medium containing the organism. The 

 latter takes up some of the stain, the amount of coloration depending 

 on the organism concerned and on the stain employed. 



The commoner intra ritam stains are pure, medicinal (zinc-free) 

 methylene blue and neutral red, used in aqueous solutions. A solution 

 of methylene blue of i per 1,000 of water may be tried, while neutral 

 red in the proportion of i per 3,000 parts of water has proved of 

 service. 



The second method of vital colouring consists in placing a drop of 

 i per cent, solution of methylene blue on a slide or cover-slip, slightly 

 spreading it, and allowing it to dry. The living organism is then 

 placed in a drop of saline on the prepared slide or cover-slip, which 

 is then mounted and examined under the microscope. Progressive 

 staining of the organism occurs and its internal structure can be seen. 

 A similar procedure may be followed for neutral red. Intra mi am 

 staining is useful for relatively large and easily deformed protozoa 

 such as ciliates, as well as for amoebae and flagellata of the gut. 



When examining very actively motile organisms, it is sometimes 



