PRACTICAL EXERCISES 



2J 7 



30. Determination of the Circulation-Time. (a) Begin with ail arti- 

 ficial scheme (Fig. 107). Fill the syringe with a 0-2 per cent, solution 

 of methylene blue. Allow the water to flow from the bottle by loosen- 

 ing the clamp. Inject a definite quantity of the methylene-blue solu- 

 tion, and with a stop-watch observe how long it takes to pass from 

 the point of injection to the end of the glass tube filled with beads 

 Make ten readings of this kind, and take the mean. Then raise the 

 bottle so as to increase the ra' e of flow of the water, and repeat the 

 observations. The ' circulation- time ' will be found to be diminished. 

 ^a This corresponds to an increase of 



, .F\^ : blood- pressure due to increased act 

 tivity of the heart, without change 

 in the calibre of the bloodvessels. 

 Next, leaving the bottle in its present 

 position, diminish the outflow by 

 tightening Ihe clamp; the circulation- 

 time will be increased. This corres- 

 ponds to an increase of blood-pressure 

 due to diminution in the calibre of 

 the small arteries. 



(b) Fill the syringe* with methy- 

 lene-blue solution (0-2 per cent, in 



Fig. 107. Artificial Scheme to illustrate a Method of measuring the Circulation- 

 Time. B, bottle containing water, the rate of outflow of which is regulated by 

 screw-clamp a; S, syringe filled with methylene-blue solution, connected with 

 T-piece A; M, beaker containing methylene-blue solution; b, c, screw-clamps; 

 C, T-piece, inserted in the course of the flexible tube E, and connected with the 

 glass tube T, which is filled with beads; F, outflow tube. The clamp c having 

 been closed and b opened, the syringe is filled with the methylene-blue solution; 

 b is then closed, c opened, and a definite quantity of the solution injected into the 

 system. The time from the beginning of injection till the appearance of the blue 

 at G is measured with the stop-watch. 



0-9 per cent, salt solution), as in (a). Keep the solution warmed to 

 40 C. by immersing the small beaker containing it in a water-bath, or 

 heating it over a Bunsen with a small flame. Weigh a rabbit or cat. 

 In the case of the rabbit, inject 1 grm. chloral hydrate into the rectum, 

 and later on give ether if necessary. If a cat, give ether alone, or 

 urethane (1-5 grm. per kilo by stomach tube i to 2 hours before). 

 Fasten it on a holder, back downwards (Fig. 61, p. 136). Cover it with 

 a towel to keep it warm. Clip off the hair on the front of the neck, and 

 make an incision i J inches long in the middle line, beginning a little 



* A burette, sloped so as to make a small angle with the horizontal, may 

 be substituted for the syringe. The burette is supported on a stand at such 

 a height (say 10-15 cm. above the level of the caiinula) that the methylene- 

 blue solution runs without great force into the jugular. The danger of pro- 

 ducing an abnormal result by suddenly raising the pressure in the right side 

 of the heart is thus avoided. 



