116 PHYSIOLOGY. 



nexion. For example, the voluntary muscles lose this [simple life] 

 much sooner than the involuntary. This is carried still further in such 

 involuntary parts as are mere appendages of the animal, among which 

 the secundines may be reckoned. I find that the umbilical artery and 

 veins of a calf will contract, after being cut, four times twenty-four hours 

 after the death of the animal, while the other arteries of the same calf 

 will not contract when cut in the same manner, after it has been 

 dead twenty -four hours. So far we find a very material difference in 

 parts of which the construction and use are the same. This experi- 

 ment was made in the winter of 1780. Probably they could not live so 

 long in the summer. However, both the experiments were made at 

 the same time, which shows the comparative powers of these two vessels 

 of the same animal. 



This principle of simple life is much more universal in one class of 

 animals, viz. the Tricoilia, than in those we have been speaking of. It 

 exists, I believe, universally through the whole of this class [Tricoilia], 

 in a much greater degree than the above [Tetracoilia], The Tricoilia 

 have also some parts of their body which are possessed of a greater share 

 of it than others, viz. the voluntary muscles, which have much less of 

 it, or lose it much sooner, when deprived of their sensation, than the 

 involuntary [muscles do] : so that this class of animals is pretty uni- 

 form one 'with another, as is the case with the first, only they have 

 more of [irritability or ' simple life '] ; but we have reasons to suppose 

 that they have less of the sensitive [life] . 



In another class of animals, viz. the Fish, which is inferior to the last, 

 this principle [of Simple Life] is not nearly so uniform through the whole 

 tribe as it is in the two above-mentioned classes. We find some fishes 

 dying instantaneously upon being deprived of the sensitive life, or that 

 upon which the sensitive immediately depends, viz. proper circulation. 

 Such is the case with mackerel upon beingtaken out of water; while others 

 will live for a considerable time when all sensation is gone, and when, 

 of course, there is a cessation of all voluntary motion : such is the case 

 with the eel, when either taken out of the water, or when its head has 

 been cut off, or its heart taken out. There is, then, a great inequality 

 in the same class of animals with respect to this principle. I shall not 

 at present pursue the subject into other classes of animals; the above 

 three classes, with the variations they admit of, are sufficient for the 

 explanation I at present can give. 



There is nothing in the nervous system, that I know, that can give 

 any light on this subject ; although it is possible that they [Simple 

 Life and Nervous System] may be immediately related, or that some 

 other principle may be the original cause [of Simple Life]. That there 



