BLOOD SPECIFIC GRAVITY, ETC. 71 



Choose a suitable short glass cannula for insertion into the femoral 

 artery and fill it with Ringer-Locke fluid. Attach clip-weights to the proxi- 

 mal and distal ligatures, so that the weights drag on the loops and thus 

 occlude the femoral above and below ; then at once, steadying the artery 

 by the distal tied thread, cut with the points of fine scissors an oblique slit 

 in the femoral about 2 mm. distal to the middle (untied) thread-loop. Insert 

 the point of the cannula through the slit into the artery with its point directed 

 towards the heart. Secure the cannula by tightening the thread-loop round 

 the neck of the cannula. 



B. Expose the external jugular of the right side (see exerc. X, § III, B) and 

 insert into it a glass cannula directed towards the heart. Bring the burette 

 containing 50 c.c. of warm Ringer-Locke within reach of the jugular cannula 

 and establish connexion free from all air-bubbles between the jugular cannula 

 and the burette by suitable rubber tubing. Allow about 5 c.c. of the Ringer- 

 Locke to flow into the jugular and then close the clamp on the rubber tube. 



III. 2. Ohservation of the sp. gr. of the hlood. Bring the test-tube rack 

 and armed pipettes to the preparation table. With a fine pipette empty as 

 much fluid as you easily can from the arterial cannula. Release proximal loop 

 on the femoral artery by moving the weight so that it no longer drags on the 

 occluding thread. The blood from the artery enters the cannula. Let it 

 overflow somewhat, and then draw up into one of the armed capillary pipettes 

 an amount of blood sufficient to rather more than fill the capillary portion of 

 the pipette. Replace the weight so that the thread again occludes the artery. 

 Keeping the free end of the rubber tubing attached to the capillary pipette 

 closed by the mouth, insert the capillary vertically into the test-tube contain- 

 ing sp. gr. fluid 1054 ; expel a minute quantity of the blood and note whether 

 as it leaves the pipette it sinks or rises in the fluid. If the latter, repeat in 

 the fluid of next lower gravity, and so on, until a fluid is found in which it 

 does not rise. The sp. gr. of the blood is thus determined. 



IV. Open the clip on the rubber tube between burette and jugular vein, Obs. 48. 

 and allow 30 c.c. of the Ringer-Locke to enter the circulation. When nearly 3)iiution of the 

 30 c.c. have entered repeat the observation on the sp. gr. of the blood. Note blood bv^^iine 

 that the sp. gr. of the blood is lower than before. After 30 c.c. has entered injection, 

 the circulation close the clamp on the burette-tube and repeat as quickly as 

 possible the observation on the sp. gr. of the blood. Then repeat observations 

 on sp. gr. of blood at intervals of 3 min. for about ten minutes. The 

 blood tends to return to its original sp. gr. Clots which form in the cannula 

 may be removed by passing a fine wire down it and through its neck into the 

 artery. 



