406 APPENDIX. 



CHAPTER XIII. 



The beat of the heart is very conveniently studied in the 

 frog. Put a live frog into a glass bowl with a piece of cottop 

 batting or of cloth saturated with chloroform and cover the 

 bowl. In a few minutes the animal will have become motion- 

 less and insensible. Remove it from the bowl ; with a sharp 

 knife divide the skin and cartilage at the base of the skull, thus 

 making an opening into the brain cavity ; into the latter thrust 

 a wire, and by twisting it about destroy the brain. The frog 

 will probably struggle, but its motions are reflex, and it has no 

 consciousness of pain. The heart may now be exposed by 

 making an incision through the skin and muscles of the upper 

 part of the abdomen and removing the cartilaginous part of the 

 breastbone. The heart will be seen beating inside the pericar- 

 dium. The latter may be removed and the heart freely exposed. 

 After studying the movements of the organ it may be removed 

 from the body by cutting the blood-vessels close to their junc- 

 tion with the heart, and placed on a plate of glass or in a watch 

 glass containing .75 per cent, salt solution. Its movements will 

 continue a long time after its removal from the body. The 

 heart may afterward be opened and the relation of its ventricle, 

 auricles, and the connecting veins and arteries studied (Fig. 76). 



The heart of the pig, sheep, or calf may be used to show the 

 structure of the mammalian heart. It is best to procure at the 

 meat-shop several " plucks " — i. e., heart, lungs, and trachea all 

 attached together. Instructions should be given the butcher 

 that the parts are to be left intact, otherwise they will be found 

 to be punctured with knife cuts. Dissect out the blood-vessels 

 for some little distance from the heart in order to get their re- 

 lations. Open some of the hearts lengthwise, others crosswise, 

 to show the internal structure (Fig. 74). Pour water into the 

 cavities to show the action of the valves. The flow of blood 

 through the heart may be illustrated by connecting the aorta 

 with the venae cavfe by means of rubber or glass tubing to rep- 

 resent the systemic circulation, and the pulmonary artery with 

 the pulmonary veins to represent the pulmonary circulation, 

 then filling the heart with water or a colored fluid and compress- 

 ing the organ with the hand (Fig. 76). 



The circulation may be studied in the web of the frog's hind- 



