Diagnosis of Malarial Fever 



503 



staining .is given in detail in the section of this work dealing with 

 "The Staining of Protozoa," q.v. 



3. Ross's Method of Finding the Parasites When Present in Small 

 Numbers. — 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 with- 

 out fixing, the sUde is stood vertically in a vessel filled with distilled 

 water. The red corpuscles at once begin to hemolyze and the process 

 is carried on to completion. When all of the hemoglobin has been 

 removed, the slide is taken out, dried, and then fixed and stained. 



! 



ACl 



Fig. 180. — A, large capillary tube (a) indicating place to cut; B, manner of draw- 

 ing out the cells and Plasmodia (Bass). 



There now being no red corpuscles to distract the attention or obscure 

 the vis'on, the stained parasites can quickly be found. 



4. Bass's Method of Concentrating the Parasites by Centrifugation. — 

 Bass and Johnsf withdraw 10 cc. of blood from a vein of the forearm 

 and mix it with 0.2 cc. of a solution of 50 grams of sodium citrate 

 and 50 grams of dextrose in sufficient water to make a volume of 

 100 cc. The blood thus prepared is placed in two centrifuge tubes 

 and whirled at a speed of 2500 revolutions per minute for one min- 

 ute. All of the Plasmodia, except the small aestivo-autumnal rings, 

 and leukocytes rise to the top of the cell sediment and are found in 

 the first 0.1 cm. With a large capillary pipet this "cream" is taken 



* l^'Lancet," Jan. 10, 1903. 

 .' t "Amer. Jour, of Tropical Diseases and Preventive Medicine," 1915, rn, 298. 



