PRINCIPAL PHYSIOLOGICAL TESTS. 25 



injected by means of a small calibrated syringe and connections into 

 the saphenous vein. The time of this injection should be registered 

 and should occupy about five seconds, and should be gently per- 

 formed. This is then rapidly followed from the same syringe with 

 1 c. c. of the normal salt solution to wash into the circulation any of 

 the solution that may be in the syringe and connections. This injec- 

 tion should occupy the same length of time and should always be 

 noted. It is important that the standard solution be made fresh at 

 each test, as otherwise it gradually loses its activity. The pupils 

 should be examined to see if there is any action, as there may be 

 bodies present in the extract which might neutralize the blood- 

 pressure-raising action. During the experiment the animal must 

 be kept warm. Not over 2 c. c. of fluid should be injected at any one 

 time, to avoid the pressor action of the large volume of fluid. The 

 action of the comparatively large amounts of fluid used in this form 

 of injection may be overcome by injecting the fluid into the vein 

 without the use of a syringe. For this injection a pipette of 1 c. c. 

 capacity accurately divided into tenth cubic centimeters is closely 

 connected to a fine, clean, sharp hypodermic needle by means of a 

 rubber tube, and after gently pushing the needle through the wall of 

 the vein toward the heart the fluid is let run into the circulation and 

 the amount controlled by the finger or, better, a burette may be 

 connected with the cannula and the injection thus made. By this 

 method it will not be necessary to use sodium chlorid solution to 

 wash the adrenalin solution into the vein. 



The most satisfactory method is to connect the syringe or, prefer- 

 ably, a burette containing the standard solution with one saphenous 

 vein and the solution to be tested with the corresponding vein of the 

 other leg, so that alternate injections of standard and unknown solu- 

 tion can be made under the same conditions. The writer's own prefer- 

 ence is for the burette method. 



The maximum rise in blood pressure from this injection, 0.001 mg. 

 per kilo, which is about 14 to 28 mm. Hg, although this will vary in 

 various dogs, is now noted, and also the distance traveled by the paper 

 and the time which elapses before the blood pressure returns to nor- 

 mal. A line running on a level with the base of the blood pressure 

 curve will aid in rapid calculation. The method of measuring the 

 blood pressure can be found in W. Stirling's Outlines of Practical 

 Physiology, third edition, 1898, page 305. 



Very dilute solutions are purposely used, so that there will be no 

 accumulation of the active principle in the animal. After five or 

 six minutes a very dilute solution, one which would approximate in 

 strength that of the normal, and diluted to the same bulk as the con- 

 trol, is similarly injected, with all the above precautions, and the 



