10 METHODS OF EXAMINATION 



The diluted blood should spread so that the erythrocytes are well 

 separated. It is not necessarj' to mix the blood and diluting fluid 

 by long stirring. Two preparations should always be made. If 

 the count varies much in the two, other preparations should be 

 made. Examination is made with an oil immersion objective. 

 A square diaphragm in the ocular, easily made of stiff paper, 

 facilitates counting. Both the blood plates and erythrocytes are 

 counted in fields taken at random in different parts of the specimen 

 until 250 to 500 erythrocytes have been seen. This will give the 

 ratio of plates to erythrocytes. The number per cmm. is obtained 

 by multiplying the number of erythrocytes per cmm. by this ratio. 

 Kemp and Calhoun's method.— Kemp and Calhoun used the 

 following diluting and fixing fluid: 



Formalin (40%) 10 cc. 



Sodium chloride (1% aq. soln.) 150 cc. 



(Color with methyl green or methyl violet if desired). 



In this method the blood comes in contact with the fixing fluid 

 before touching anything else. The site of puncture is carefully 

 cleaned and dried. Puncture is made, the first drop wiped off and 

 diluting fluid placed on the site of puncture so that the next drop 

 as it emerges flows into the diluting fluid. Mix thoroughly for a 

 few seconds with a clean glass rod then transfer a large drop with 

 the glass rod to the Thoma counting chamber and cover with a 

 thin cover glass. If the corpuscles are fairly evenly distributed, 

 let the chamber rest quietly for about five minutes. Count the 

 red corpuscles and blood plates in about six frames of 16 squares 

 each. This usually gives about 100 blood plates. With a small 

 number of blood plates or with not so even a distribution more 

 than six frames should be counted. The number per cmm. is 

 obtained by multiplying the number of erythrocytes, obtained in 

 the usual manner, by the ratio of blood plates to erythrocytes. 



Wright and Kinnicutt's Method.— The diluting fluid is com- 

 posed of two parts of an aqueous solution of "brilliant cresyl blue " 

 (1 :300) and three parts of an aqueous solution of potassium cyanid 

 (1:1400). These two solutions must be kept in separate bottles 

 and mixed and filtered immediately before using. 



The blood is diluted 1:100. The process should be done as 

 rapidly as possible. Count in the ordinary counting chamber, 

 using a high power dry objective. The authors used the thin 



