I7 A MANUAL OF PHYSIOLOGY 



expose about four costal cartilages (say, 3rd to 6th). With a curved 

 needle pass waxed ligatures round the cartilages, and tie firmly to 

 compress the intercostal vessels. Then pass a waxed ligature under 

 the upper portion of the sternum, and tie it very tightly round that 

 bone so as to occlude the internal mammary arteries. The bellows 

 should now, or earlier if any symptoms of impeded respiration have 

 appeared, be connected with one end of the horizontal limb of a 

 glass T-piece, the other end of which is similarly connected with the 

 tracheal cannula. The stem of the T-piece is provided with a short 

 piece of rubber tubing, which, when artificial respiration is being 

 carried on, is to be alternately closed and opened closed during 

 inflation of the lungs, and opened when the air is to be allowed to 

 escape from them. Ether may, if necessary, be administered by 

 passing this short tube through one neck of a WoulrFs bottle con- 

 taining the anaesthetic, and alternately compressing and opening it as 

 described. If the cannula has a side-opening, as is usually the case 

 with metal cannula?, the T-piece may be dispensed with. One 

 student should take sole charge of the artificial respiration, which 

 ought to be begun as soon as the chest has been opened, and con- 

 tinued at the rate of about twenty inflations per minute. The costal 

 cartilages and sternum are rapidly cut through with strong scissors 

 just on the sternal side of the ligatures, and the sternum is divided 

 below its ligature, the artificial respiration being suspended for an 

 instant, as each cut is made, to avoid wounding the lungs. The 

 lower part of the sternum is turned down like the lid of a box, tied 

 out of the way or cut off altogether, and the heart, enclosed in the 

 pericardium, comes into view. If the ligature round the sternum has 

 not properly compressed the internal mammary arteries, haemorrhage 

 from the central ends may now occur. In this case they must be 

 seized with artery-forceps and ligatured. A cotton thread is now 

 passed with a suture-needle through each side of the pericardium, 

 which is then stitched to the chest-wall and opened. The following 

 observations and experiments should now be made : 



(a) Note the various portions of the heart, right and left ventricles, 

 right and left auricles, with the auricular appendices. Feel the heart 

 with the hand, and observe that the right ventricle is softer and has 

 thinner walls than the left, and that the auricles are softer than the 

 ventricles. Note how all the parts of the heart harden in the hand 

 during systole and soften during diastole (pp. 74-76). 



(b) Dissect out the vago-sympathetic on one side in the neck of 

 the dog. The guide to the nerve is the carotid artery. These two 

 structures and the internal jugular vein lie side by side in a common 

 sheath. Feel for the artery a little external to the trachea, cut down 

 on it, open the sheath, isolate the vago-sympathetic for about an 

 inch, pass two ligatures under it, tie them, and divide between the 

 ligatures. The peripheral and central end of the nerve may now be 

 successively stimulated. Stimulation of the peripheral end causes 

 slowing of the heart or stoppage in diastole. Feel that it softens 

 when it .stops. It soon begins to beat again. Stimulation of the 

 central end of the vago-sympathetic may or may not cause inhibition. 



