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XV. Theory of the inverse Ratio which subsists between the Respiration and 
Irritability, hi the Animal Kingdom. By Marshall Hall, M.D. F.R.S.E. 
M.R.I. 8$c. 8$c. Communicated by J. G. Children, Esq. Sec. R.S. 
Read February 23, 1832. 
The object of the investigation, of which the present paper details the prin- 
ciples, is to trace a peculiar law of the animal economy, through the various 
series, forms and conditions of animated being. This law may be announced 
in the following terms : 
The quantity of the Respiration is inversely as the degree of the Irritability of 
the muscular fibre. 
It will be necessary, in the very first place, to define the terms which I 
am about to employ. The expression inverse ratio is not used in its strict 
mathematical sense, but merely to designate the general fact, that, in cases in 
which the quantity of respiration is great, the degree of irritability is low ; 
and that in cases in which the quantity of respiration is small, the degree of irri- 
tability is high. By the quantity of respiration, I mean the quantity of oxygen 
gas consumed, or exchanged for carbonic acid, in a given time, by the animal 
confined in atmospheric air. I have used the term irritability in the sense in 
which it is employed by Glisson and Haller, — to designate that peculiar pro- 
perty of the muscular fibre by which it contracts on the application of an 
appropriate stimulus ; and I consider that muscle the most irritable which, 
cseteris paribus, contracts most and longest upon the application of the least 
degree of such stimulus. Haller’s definition of the term is very similar *. 
It must be confessed that the word irritability only expresses one half of the 
property or function of the muscular fibre, — its susceptibility to the influence 
of irritants or stimuli ; the term contractility is equally defective, — expressing 
* M6moires sur la Nature sensible et irritable des Parties du Corps animal. Tome i. pp. 7 — 8, 75. 
