WHICH SUBSISTS BETWEEN THE RESPIRATION AND IRRITABILITY. 331 
sion of respiration such an animal would not drown though immersed in 
water. Now there is precisely such a case. It is that of the hybernating 
animal. It will be shown in the subsequent paper, that in the state of 
perfect hybernation the respiration is nearly suspended; the blood must, 
therefore, be venous. Yet the heart continues to contract, although with 
a reptile slowness. The left ventricle is, therefore, veno-contractile, and in 
this sense, in fact, sub-reptile. The case forms a sole exception to the law 
pointed out by Harvey, that the left ventricle ceases to contract sooner than 
the right. If in the hybernating animal the left ventricle does cease to beat 
sooner than the right, it is only in so slight a degree as to be referred to the 
greater thickness of its parietes, and the slight degree in which respiration 
still remains. It is obvious that the foregoing statement must be taken with 
its due limitations. Venous blood is unfit for the other animal purposes, even 
though it should stimulate the heart to contraction. 
Another mode of determining the degree of irritability, is the application of 
stimuli, as galvanism. A muscular fibre endued with high irritability, as that 
of the frog, and the galvanic agency are mutually tests of each other*. 
A third criterion and measure of the irritability is afforded by the influence 
of water at temperatures more or less elevated, in inducing permanent con- 
traction of the muscular fibre. 
There are two other properties of animals which depend upon the varied 
forms of the inverse ratio which exists between the respiration and the irrita- 
bility. The first is activity , the second, tenacity of life. 
Tbe activity, which, I believe, M. Cuvier has confounded with the irrita- 
bility, is generally directly proportionate to the respiration, and intimately 
depends upon the condition of the nervous system resulting from the impres- 
sion of a highly arterial blood upon its masses, and not upon the degree of 
irritability of the muscular fibre. It is the pure effect of high stimulus. 
To show that M. Cuvier has blended the idea of the irritability of the muscu- 
lar fibre with that of the activity of the animal, it is only necessary to recur to 
the passages already quoted from that author, and to adduce the observations 
* Bostock on Galvanism, pp. 4, 14. 
