188 LOCOMOTION. [CHAP. vn. 



by their both interfering with healthy nutrition. That they do thus 

 act, is rendered probable by other proofs. It has long been known 

 that cutting off the supply of blood from a muscle destroys its 

 contractility ; that unnatural temperature has the same effect ; and, 

 in general, that all causes affecting nutrition affect also contrac- 

 tility in the same degree. 



The contractility of a muscle has also invariably a certain com- 

 plexion or character connected, we might almost say, with the vigour, 

 but at least with the character, of the nutrient process in the parti- 

 cular muscle. This fact has been ably illustrated by Dr. Marshall 

 Hall,* who nevertheless is opposed to the great conclusion which 

 we consider to flow from it, that contractility is proportioned to 

 the activity and perfection of the nutrient function. 



If we suddenly check the supply of nutrient material to the mus- 

 cles of various animals, in the same state as regards previous stimu- 

 lation, and in such a manner as not to stimulate the muscles in so 

 doing ; we shall find that their contractility, as evidenced by their 

 contracting under a given stimulus, endures through very unequal 

 periods of time. Thus, in the bird it is very evanescent ; in the 

 insect, also, it is very evanescent ; in the mammal less so ; in the 

 reptile it lingers longer ; while in the fish and crustacean it is in 

 general very enduring. 



The degree in which oxygen is admitted to the tissues in these 

 animals, corresponds in the main with the scale thus designated by 

 the relative endurance of the contractility of their muscles. No- 

 thing is more probable than that the amount of oxygen admitted to 

 the tissues may be taken as a fair estimate of the activity in them 

 of the processes of waste and assimilation. Now, we know that the 

 vitality of the tissues does not cease immediately on their supply of 

 nutriment being cut off ; that death of the whole animal, as an indi- 

 vidual, is not necessarily attended with simultaneous death of every 

 part ; that somatic death gradually follows systemic death, from the 

 functions being no longer concatenated in mutual dependence : 

 and it is entirely consonant with facts, to suppose that the endur- 

 ance of the vital functions in the tissues after systemic death is pro- 

 portionate to the slowness with which they are ordinarily performed. 

 The close correspondence, therefore, between the duration of con- 

 tractility and the slowness of the nutrient function in various 

 animals, is a strong evidence of the dependence of the one on the 

 other. 



See article " Irritability," Cyclop, of Anat. and Phys. 





