CHAPTER XX 

 Study of the Circulation in Mammals 



Study of blood-pressure, and the effects of nerves and drugs upon 

 the heart and arteries in animals. Either an anaesthetised animal, 

 rabbit or cat, may be employed as the subject of a demonstration on 

 blood-pressure, or a " Sherrington " preparation (p. 81) can be used by 

 the student. A cannula (Fig 67, e) is inserted into one of the 

 carotids towards the thorax and tied securely in. If a dog is used 

 the femoral artery may be employed instead of the carotid. The 

 artery is previously ligatured above and clamped below the place of 

 insertion. The cannula is connected by a tube containing a half -satur- 

 ated solution of sodium bicarbonate with the proximal limb of a 

 mercurial manometer; a lateral tube affords communication with a 

 reservoir of the same solution, which is under pressure. By this 

 pressure the mercury is forced up in the distal limb of the manometer, 

 so that the recording style is about 50 mm. above the abscissa or zero 

 line. The clamp on the artery is then removed, and a record of the 

 arterial pressure taken, a time record (in minutes or fractions of a 

 minute) being also inscribed. It is useful to record the respiratory 

 movements at the same time by tambours. A blunt metal cannula, 

 which fits the nozzle of a hypodermic syringe, is tied into one of 

 the jugular or femoral veins towards the thorax: this is for the 

 purpose of giving intravenous injections of drugs and extracts. A 

 kidney, or the spleen, or a loop of intestine, or a limb, may be placed in 

 a plethysmograph, and the changes of volume recorded. In the 

 anaesthetised animal the following experiments can be made : for many 

 of them the Sherrington preparation may be used : 



1. Effect of exciting the afferent fibres of a peripheral limb-nerve. 

 Expose any limb nerve, tie a ligature tightly round the distal end of 

 the part exposed. Stimulate the central end. Observe the effects on 

 arterial pressure, on heart rate, and on respiration. 



2. Put a drop or two of amyl nitrite on cotton- wool and allow the 

 animal to inhale the vapour. Note the effect on blood- pressure. 



3. Effect of exciting the vagus. One of the vagi in the neck having 



