EXAMINATION OF THE BLOOD 771 



In certain cachectic conditions the parasites are also found in the blood in the 

 intervals between the attacks of fever, but as a rule they disappear from the peri- 

 pheral blood during apyrexial intervals especially when the patient is being treated 

 with quinine. The crescent form of the parasite is more resistant to this drug 

 than the other forms. 



It is best to examine the blood in the fresh state. 



(a) Examination of fresh blood. The patient's finger is well washed with 

 soap and water and then with alcohol to remove the fatty secretions from the 

 skin. The pad of the finger is then pricked with a sterilized needle and 

 after wiping away the first drop of blood with a piece of soft linen a small 

 drop is collected on each of a series of scrupulously clean glass slides and 

 immediately covered with a cover-glass. 



Should the drop of blood be rather large, gentle pressure may be applied 

 to the cover-glass and the blood so squeezed from beneath it wiped away : 

 in this manner a very thin layer of blood is obtained in which the red cells 

 are lying flat and not piled one upon another in rouleaux. In the majority 

 of cases no advantage is gained by ringing the cover-glass with paraffin, 

 because the blood will coagulate at the edges and afford sufficient protection 

 against evaporation : but in studying the movements of the parasites it is 

 well to adopt this precaution so that the movement imparted to the red cells 

 by the evaporation taking place at the edge is avoided. The preparation 

 ought to be examined with an high power dry objective. 



The living parasite may be stained in the following manner. A drop of methylene 

 blue in 0'75 per cent, normal saline solution is placed on the slide by the side of 

 the drop of blood. A cover-glass is lowered on to the two drops which mix with 

 the result that the parasites soon take up the dye which is not toxic to them 

 and then stand out more sharply against the unstained background (Neveu-Lemaire). 

 Celli and Guarnieri use a solution of methylene blue in ascitic fluid for the purpose. 



(/3) Examination of dried films. Blood dried on cover-glasses may also 

 be used for investigating the presence of hsematozoa and studying their 

 characters. The films may be prepared on cover-glasses in the ordinary way, 

 though sometimes it is preferable to spread the blood on slides in the following 

 manner : A little drop of blood is placed at one end of a slide and spread 

 with the edge of another slide a visiting card or cigarette paper will do 

 as well by drawing the latter rapidly towards the other end of t'he slide 

 with a single uninterrupted motion (p. 204). The preparation is dried as 

 rapidly as possible in the air and then fixed in alcohol-ether or, better, in 

 absolute alcohol for 10-20 minutes. Fixation by heat is too crude and 

 altogether unsuitable. 



To examine dried preparations unstained the films on the cover-glasses are 

 simply laid on a slide and fixed by their edges with paraffin. 



Methods of staining. The Hsematozoa may be stained with various dyes, 

 methylene-blue, gentian-violet, violet-dahlia and Boehmer's haematoxylin 

 being especially useful. 



Blood films prepared as above on slides or cover-glasses may be stained by 

 one of the following methods. 



1. Methylene Blue. (a) The film is stained for 30 seconds in a saturated 

 aqueous solution of methylene blue, washed, dried and mounted in balsam. 

 The red cells are unstained, the nuclei of the leucocytes appear deep blue and 

 the parasites pale blue. 



Hanson recommends the use of Loaffler's alkaline blue (p. 139). Koch prefers 

 borax blue (borax 5 grams, distilled water 100 c.c. methylene blue 2 grams). Stain 

 for 30 seconds, wash in water, dry and mount in balsam. 



(b) Stain in 0'5 per cent, solution of eosin, then in an aqueous solution of 



