PRACTICAL EXERCISES 189 



soon as the injection is finished, draw off a sample of 5 c.c. of blood 

 into a test tube labelled C, and let it stand. In ten minutes collect 

 three further samples of 5 c.c., D, E, and F, and a large one G ; in 

 half an hour another set of three small samples, and at as long an 

 interval as possible thereafter three more. Add to E 15 drops of a 

 2 per cent, solution of calcium chloride, to F 5 c.c. of a solution of 

 fibrin ferment containing some calcium chloride, and put D, E, and 

 F into a water-bath at 40. Treat the other sets of small samples in 

 the same way, and also the plasma obtained by centrifugalising G. 

 Note how long each specimen takes to clot, and report your results.* 

 23. Effect of Suprarenal Extract on the Blood-Pressure. Make 

 the arrangements for a blood-pressure tracing from a dog as in 1 9, 

 p. 1 85. Put a cannula in the carotid and another in the femoral vein 

 or one of its branches (p. 177). Expose both vagi in the neck, and 

 pass threads loosely under them. Connect the carotid with the mano- 

 meter and take a tracing. Then, while the tracing is continued, 

 inject slowly into the femoral vein an amount of watery extract 

 corresponding to about -Jth gramme of suprarenal. The blood- 



FIG. 74. EFFECT OF INJECTION OF PEPTONE ON THE BLOOD-PRESSURE 

 IN A DOG. (TO BE READ FROM RIGHT TO LEFT.) 



pressure risesf owing to constriction of the arterioles by direct action 

 of the extract on their muscular tissue. The heart is greatly slowed 

 owing to stimulation of the cardio-inhibitory centre. At once cut 



* Sometimes the injection of peptone hastens coagulation instead of 

 hindering it. It has been asserted that this is only the case when small 

 doses are used (less than 0*02 gramme per kilo of body- weight). But in 2 

 dogs out of 1 1 a dose of 0-5 gramme per kilo has been seen to hasten coagu- 

 lation, and in I out of 12 to leave it unaffected; in the other 9 coagulation 

 was markedly retarded. The blood-pressure always fell, the amount of 

 the fall varying from 81 to 21 mm. of mercury (average, 60 mm.). It 

 sometimes returned to normal in twenty to thirty minutes, but usually 

 required a longer time. 



f The amount of the initial rise of pressure is very variable, since the 

 slowing of the heart tends to diminish the pressure, while the constriction 

 of the arterioles tends to increase it. Thus, in one experiment the increase 

 of pressure on injection of the extract was only 6 mm. of mercury, while 

 in another it was 56 mm. On section of the vagi in this second experi- 

 ment, there was an additional rise of 64 mm., and after a second injection 

 a further rise of 70 mm., making an increase of 190 mm. in all above the 

 original pressure. 



