22 METHODS OF EXAMINATION 



After bringing the specimen into focus, using the 2 mm. objec- 

 tive and the x 1 ocular, and before beginning to make the count. 

 it is well to examine a few leucocytes to see how the stain has taken 

 in this specimen. After beginning the count determine the variety 

 to which each leucocyte belongs and record it in the appropriate 

 column. In making the count move the slide so the field of view 

 travels across the width of the film moving back and forth until 

 the entire film or the desired number of leucocytes has been ex- 

 amined. With a mechanical stage one need move to the right or 

 left on reaching the edge of the film only the width of the field of 

 view, which is easily determined by noting a corpuscle at the ex- 

 treme edge of the field and then moving the slide so that this 

 corpuscle just disappears on the opposite side of the field; but 

 without a mechanical stage one must allow some space to avoid 

 the danger of running into the track previously examined and 

 counting some leucocytes twice. When a sufficient number of 

 leucocytes has been examined the percentage of each variety is 

 determined by dividing the number of each variety by the total 

 number counted. For example, suppose a specimen of horse's 

 blood was examined and was found to have 119 lymphocytes, 

 26 large mononuclears, 338 polymorphs, 16 cosins and 1 mast 

 cell. The total number examined was 500, then -g^ = 23.8% 

 lymphocytes, ^„ = 5.2% large mononuclears, J~ = 67.6% 

 polymorphs, ^ = 3.2% eosins, -5^ = 0.2% mast cells. It is 

 well to add the percentages to see if they make 100 or nearly that. 

 It is not necessary to give the percentage for more than one decimal 

 place. 



TEST FOR GLYCOGEN 



In making a test for glycogen in the blood, smears are made 

 in the usual manner and are allowed to dry in the air. A drop of 

 the following solution is placed on the film which is then covered 

 with a cover glass. 



Iodine 1 grain. 



Potassium iodide 3 gins. 



Distilled water 100 cc. 



Add powdered gum arabic, about 50 gms., sufficient to produce a syrupy 



fluid. 



Examine with a two mm. oil immersion objective after four 



