WHICH SUBSISTS BETWEEN THE RESPIRATION AND IRRITABILITY. 333 
being greatest of all in those animals which approach a mere muscular struc- 
ture. Almost the sole vital property then remaining is the irritability; and 
this property does not immediately suffer from division. 
It is possible to reduce some of the reptile tribes to a state approaching that 
of animals still lower in the scale, by removing, by very slow degrees, suc- 
cessive portions of the nervous masses. This is most readily done in animals 
in which the respiration is already low, and the irritability high, as in the foetus, 
in the very young animal, in the reptile, &c., as in the experiments of Legal- 
lois*, M. Serres-}-, myself;};, &c. 
There is, even in animals most tenacious of life, one kind of mutilation — 
one kind of injury not well borne. As the blood is in its lowest condition of 
stimulus, it cannot be withdrawn with impunity ; frogs even soon perish if 
their blood be allowed to flow. As the irritability, on the other hand, is high, 
certain stimuli, as galvanism, slightly elevated temperatures, & c. are speedily 
fatal. The batrachia are promptly destroyed by immersion in water of a tem- 
perature of 108° of Fahr., and some fish and Crustacea perish in great numbers 
under the influence of a thunder-storm. It is a singular fact, that the fish 
alone, whose food is found amongst animals of a high irritability, should pos- 
sess an electrical organ for the destruction of its prey. 
Having stated the law of the inverse ratio of the quantity of respiration, and 
of the degree of irritability of the muscular fibre, especially in the heart, I 
purpose to trace it, by a series of observations, through the zoological scale, 
and in the different stages and states of animal existence. This inquiry will 
be followed by an investigation into the quantity of respiration, in different 
temperatures and seasons, in animals which retain, and animals which lose 
their temperature ; it is obvious, a priori, that the former must have a lower 
respiration in the elevated temperatures of summer than in winter, whilst the 
irritability, and with it the power of supporting the privation of air, will ob- 
serve an inverse ratio ; in the latter, it is probable that other laws prevail. 
* Experiences sur le Principe de la Vie. f Anatomie Comparde du Cerveau, tome ii. p. 224. 
X Essay on the Circulation, chap. iii. § 1. 
MDCCCXXXII. 2 X 
