332 
DR. MARSHALL HALL ON THE INVERSE RATIO 
with which they are connected. “ On vient de voir a quel point les animaux 
vertebras se resseinblent entre eux; ils ofFrent cependant quatre grandes subdi- 
visions ou classes, caract^risees par l’espece ou la force de leurs mouvements, 
qui dependent elles-memes de la quantite de leur respiration, attendu que c’est 
de la respiration que les fibres musculaires tirent l’tmergie de leur irritabilite 
“ Comme c’est la respiration qui donne au sang sa chaleur, et a la fibre la sus- 
ceptibility pour l’irritation nerveuse, les reptiles ont le sang froid, et les forces 
musculaires moindres en totality que les quadruples, et a plus forte raison 
que les oiseaux ; aussi n’exercent-ils guere que les mouvements du ramper et 
du nager ; et, quoique plusieurs sautent et courent fort vite en certains mo- 
ments, leurs habitudes sont gtineralement paresseuses, leur digestion exces- 
sivement lente, leurs sensations obtuses, et dans les pays froids ou temp6res, 
ils passent presque tous l’hiver en lethargie -f-.” 
It is extraordinary that M. Cuvier should have associated the elevated tem- 
perature of the blood with a high irritability of the muscular fibre, when they 
are uniformly separated in nature, and are, indeed, absolutely incompatible 
in themselves. The muscular fibre of the frog is so irritable, that it would 
instantly pass into a state of rigid and permanent contraction, if bathed with 
a fluid of the temperature of the blood of birds^. 
The same confusion of ideas on the subject of the activity of the animal and 
the irritability of the muscular fibre prevails, I believe, amongst our own phy- 
siologists ; at least, in conversation with two, who may rank amongst the first, 
I found that they had uniformly considered the respiration and the irritability 
to be directly, instead of inversely, proportionate to each other. 
That singular and interesting property of the lower orders of animals termed 
tenacity of life is, on the other hand, distinctly associated with a high degree of 
irritability of the muscular fibre. This property may be defined as consisting 
of the power of sustaining the privation of respiration, the privation of food, 
various mutilations, divisions, & c. It is greater as we descend in the zoological 
scale. As activity depends upon the presence and condition of the spino-cere- 
bral masses acted upon by arterial blood, tenacity of life depends upon the 
diminution or absence of these masses and of this highly arterialized blood, 
* Lc It&gne Animal, tome i. pp. 56, 57. 2 me edit. f Ibid, tome ii. pp. 1, 2. 2 mc edit. 
; See An Essay on the Circulation, chap. vii. pp. 180, 181. 
