78 SPECIAL PHYSIOLOGY 



strip of dry cotton and a towel may be placed outside of the tannic 

 acid cotton. 



Before proceeding farther, note that the left lung is collapsed. 

 Begin artificial respiration, continuing the rhythm observed in the 

 animal. 



Carry the incision transversely across the thorax just posterior 

 to the end of the sternum; catch the cut-off internal mammary 

 arteries with haemostatic forceps; carry the incision forward along 

 the right side to correspond with the incision already made on the 

 left side, and stop the hemorrhage in the same way. 



The sternum may be covered with absorbent cotton and a towel 

 and tipped forward out of the way. 



The heart is now clearly exposed within its pericardium, and its 

 relation to other structures of the thoracic cavity may be carefully 

 noted before the pericardium is removed. 



4. Observations. (1) Note position of heart with relation to 

 lungs, spinal column, diaphragm, oesophagus, trachea, and large 

 bronchi. 



(2) Note character of pericardium and its attachments. Remove 

 the pericardium by making a free longitudinal incision with scissors 

 and slipping the heart through the incision. Note character of 

 inner surface of pericardium; of outer surface of heart; presence 

 of liquid in the pericardium. 



(3) Note sequence of contraction of the chambers of the heart. 



(4) Note change of shape of the heart during several phases of 

 a cardiac cycle. 



(5) Note change of position of the heart apex during phases of 

 a cardiac cycle. 



(6) Hold the beating heart in the hand and note the change in 

 the tension of the heart muscle during phases of cardiac cycle, 

 comparing diastole with systole. 



(7) With calipers and rule measure carefully changes in the 

 diameters of the heart, comparing end of diastole with the end of 

 systole and observing the lateral diameter and the dorsoventral 

 diameter. 



(8) Is there a change in the anteroposterior diameter base to 

 apex? If so, when does this change occur? 



(9) "Push the anaesthetic" to the limit and note that the animal's 

 heart continues to beat. The same amount of ether or chloroform 

 administered under ordinary conditions would cause the death of 

 the animal through the stopping of respiration. But the respiration 

 being carried on artificially, the amount of chloroform which can 

 be taken is much increased. In the case of the dog, it will be hardly 

 possible to kill with chloroform so long as respiration is kept up. 

 If the respiration be stopped the animal will die very soon in con- 

 vulsions. 



