PRACTICAL EXERCISES 7 



solution made by dissolving sodium citrate in Ringer's solution to the 

 extent of- 2 per cent. The solution is prevented from escaping by a 

 clip on the tube. The cannula is inserted into the carotid of a dog, 

 the end of the rubber tube dipped below a quantity of citrate- 

 Ringer solution in a beaker, and a volume of blood equal to that of the 

 solution run in. Then the blood and solution are at once stirred gently, 

 but sufficiently to insure proper admixture. 



Some blood is now run into another vessel, defibrinated, and 

 measured. An equal volume of the citrate-Ringer solution is added to 

 it while the mass of fibrin is still floating in the blodd. After mixing, 

 the fibrin is removed. Plasma is then separated by the centrifuge from 

 the first specimen of blood, and serum from the second, and comparison 

 experiments are made with each on artery rings. If the plasma has 

 been properly obtained, it will have little constrictor effect on the 

 rings in comparison with the serum. In making the comparison, 

 arteries which give a decided effect with serum should be employed. 

 The defibrinated blood and the unclotted citrate blood may also be 

 used for the comparison. 



Fig. 18. Thoma-Zeiss Haemocytometer. M , mouthpiece of tube G, by which 

 blood is sucked into S; E, bead for mixing; a, view of slide from above; b, in 

 section; c, squares in middle of B, as seen under microscope. 



10. Enumeration of the Blood - Corpuscles. Use the Thoma-Zeiss 

 apparatus (Fig. 18). (i) Suck a drop of ox or dog's blood up into 

 the capillary tube 5 to the mark i. Wipe off any blood which 

 may adhere to the end of the tube. Then fill it with 3 per 

 cent, sodium chloride to the mark 101. This represents a dilution of 

 100 times. Mix the blood and solution thoroughly, then blow put a 

 drop or two of the liquid to remove all the solution which remains in 

 the capillary tube. Now fill the shallow cell B with the blood mixture. 

 Put the cover-glass on, taking care that it does not float on the liquid, 

 but that the cell is exactly filled. Put the slide under the microscope 

 (say Leitz's oc. III., obj. 5), and count the number of red corpuscles 

 in not less than ten to twenty squares. Sixteen squares is a good 

 routine number. The greater the number of squares counted, the 

 nearer will be the approximation to the truth. Now take the average 

 number in a square. The depth of the cell is ^ mm., the area of each 

 square jj^ sq. mm. The volume of the column of liquid standing 

 upon a square is 1T ^ cub. mm. One cub. mm- of the diluted blood 

 would therefore contain 4,000 times as many corpuscles as one square. 

 But the blood has been diluted 100 times, therefore i cub. mm. of the 



