MICROSCOPIC STRUCTURE OF THE BLOOD. 273 



strument. It consists of a pipet with mouthpiece and tubing 

 connecting the two. It is carefully graduated, and has a bulb 

 which contains 100 times as much as the capillary tube when 

 filled to mark 1. In this bulb is a glass bulb which aids in the 

 mixing of the blood and saline solution. There is also a glass" 

 slide (Fig. 145, 2) having a covered disk. On the surface of this 

 1 cu.mm. is divided into 400 squares, each -fa mm. This is 

 surrounded by a cell of such height that when a cover-glass is 

 placed upon it its under surface will be fa mm. above the disk. The 

 finger being pricked, the blood is drawn into the capillary tube as far 

 as 1 on the scale ; the saline solution, Hay em's fluid (see below) or 

 3 per cent, sodium chlorid solution, is then drawn up to 101. The 

 pipet is then shaken so as to mix the blood and solution thoroughly, 

 and a drop of the mixture placed on m and covered with a cover- 

 glass. The volume of blood above each of the squares will be ^fa-$ 

 cu.mm. The corpuscles in from 10 to 20 squares are counted, and by 

 dividing this number by the number of squares taken, the average 

 per square will be obtained. This, multiplied by 4000 X 100 

 equals the number of corpuscles in a cubic millimeter of blood. 

 For the depth of the cell being -fa mm., and the area of each 

 square being ^- - sq.mm., the volume of blood on each square 

 would be ^^ cu.mm. Inasmuch as the blood has been diluted 

 100 times, 1 cu.mm. of blood withdrawn from the vessels 

 would contain 400,000 times the corpuscles in 1 square. 



Hayem's fluid consists of sulphate of sodium, 5 grams ; sodium 

 chlorid, 1 gram ; corrosive sublimate, 0.5 gram ; dissolved in 200 

 c.c. of distilled water. 



Oliver's Hemacytometer (Fig. 146). This apparatus consists 

 of a measuring pipet, a; a dropper, b ; a mixing tube, c. A small 

 amount of blood is measured in the measuring pipet and mixed in 

 the mixing tube with Hayem's fluid. The tube is then held 

 between the fingers, and the light of a wax candle, held about 2 

 meters from the eye, in a dark room, is looked at, the tube being 

 held edgeways. Enough fluid is added to make the flame appear 

 as a bright line through the mixture. If the red corpuscles are 

 present to the number of 5,000,000 to the cubic millimeter, the 

 surface of the mixture will stand at 100. If the number is less, 

 it will not require so much of the fluid to make the mixture trans- 

 parent ; while if the number is in excess of normal it will require 

 more. The graduations on the tube are percentages of the normal 

 standard ; thus if 100 represents 5,000,000 corpuscles, 80 would 

 represent 4,000,000. 



Many observations have shown that the number of red corpus- 

 cles is subject to considerable variation even in the same individual. 

 Muscular exercise, and even massage, which is passive exercise, 

 increase the number ; while food diminishes it. 



The blood of persons living in high altitudes has shown the 



18 



