OF VITAL MOTION. Ill 



tissues with which it comes in contact. And, further, 

 if the air finds entrance into the heart by this means, 

 it follows that it will be less able to retain its position 

 after a portion of its vivifying ingredients have been 

 expended, as they must have been if the diastole is 

 induced in this manner, and we may infer, therefore, 

 that the systole will occur and expel the air, as the 

 natural consequence of the altered and deteriorated 

 quality of this air. But let the explanation be as it 

 may, we may return to the original assertion, and 

 say, that there is no more proof that the air excites 

 the systole than the diastole. The question, however, 

 is extremely complicated, and we must be content to 

 deduce an indirect answer from the more evident 

 operation of intra-organic agents. 



2. Of intra-organic force as the agent in the hearfs 

 action. 



(a.) Of the nervous influence as an agent. 



The effects of fear upon the heart are very well 

 marked, and these may serve as the first subject for 

 inquiry. In this state the extreme pallor of the skin 

 and the tendency to evacuation in the several visceral 

 cavities, argue, as we have seen, an actual contraction 

 in the rudimentary muscular structures, and it is the 

 same also in the walls of the heart. When, for 

 example, fear verges upon syncope, and the contrac- 



