INTRODUCTION. 15 



Death may be either systemic or local. This is a direct 

 result of the composition of the body of cells bound to- 

 gether to form a complicated mechanism. Local death is 

 of two kindsj molar and molecular. In the latter form 

 cells die by themselves and at different times, and thus a 

 gradual loss of tissue occurs ; the former results when a 

 number of cells and other tissue elements simultaneously 

 succumb to some injurious influence. Ulceration is 

 molecular, ^gangrene is molar death. Local death 

 results from systemic as soon as the amount of nutritive 

 material supplied to each tissue by the last blood which 

 entered it has been exhausted. So the most active tissues 

 die most readily, while less highly-organised parts retain 

 vitality for some time after systemic death. It must be 

 remembered also that the life of each part of the body 

 varies in its duration,and that in the course of life of such 

 an individual as an ox, every element of a tissue is not 

 always the same, but consists of a number of short-lived 

 minute bodies which succeed one another. The blood is the 

 most important bond of connection between all the body- 

 cells. Of the value of the nervous system in this respect we 

 are not so assured. The action of each cell depends upon 

 a due supply of fresh blood containing nutritive matter. 

 Cessation of the circulation of the blood is in every case 

 the immediate cause of death. " The failure of the heart 

 may arise in itself, on account of some failure in its nervous 

 or muscular elements, or by reason of some mischief affect- 

 ing its mechanical working. Or it may be due to some 

 fault in its internal medium, such for instance as a want 

 of oxygenation of the blood, which in turn may be caused 

 by either a change in the blood itself, as in carbonic oxide 

 poisoning, or by a failure in the mechanical conditions of 

 respiration, or by a cessation of the action of the respira- 

 tory centre. The failure of this centre, and, indeed, that 

 of the heart itself, may be caused by nervous influences 

 proceeding from the brain, or brought into operation by 

 means of the central nervous system ; it may, on the other 

 hand, be due to an imperfect state of the blood, and this 

 in turn may arise from the imperfect or perverse action of 



