WHICH SUBSISTS BETWEEN THE RESPIRATION AND IRRITABILITY. 327 
trough, to pour a little water over the mercury exterior to the jar. The appa- 
ratus is thus rendered perfectly air-tight, which is not always effected by the 
mercury alone. 
By means of this apparatus we readily and accurately determine the quan- 
tity of the respiration of any given animal, in any given circumstances. 
II. Of the Measure of the Irritability. 
The problem to be next determined is that of the degree of irritability of 
the muscular fibre, and especially of the heart. This question is beset with 
scarcely fewer or less difficulties than that of the quantity of respiration, 
whilst it involves far greater errors and more discrepancy of opinion on the 
part of physiologists. 
Even Baron Cuvier* has fallen into these errors. It will be shortly demon- 
strated that the degree of irritability is, in every instance, inversely as the 
quantity of respiration. Yet M. Cuvier, in a remarkable paragraph, states 
the very contrary, and even speaks of that which is the exhauster, as the re- 
pairer, of the irritability; whilst, on the other hand, he makes statements which 
appear to me at variance with this very opinion. In the Anatomie Comparee 
(tome i. p. 49), this celebrated writer observes, “ Les experiences modernes ont 
montr6 qu’un des principaux usages de la respiration est de ranimer la force 
musculaire, en rendant a la fibre son irritabilite epuisee.” See also tome iv. 
p. 301. Similar observations are made in M. Cuvier’s more recent work, the 
R&gne Animal : “ C’est de la respiration que les fibres musculaires tirent l’ener- 
gie de leur irritabilite.” tome i. p. 5 7. 2 me edit. “ C’est la respiration qui donne 
au sang sa chaleur, et a la fibre la susceptibilite pour l’irritation nerveuse.” 
tome ii. p. 1. On the other hand, speaking of the mollusca, (tome iii. p. 3.) 
M. Cuvier observes of those animals of low respiration, “ L’irritabilite est 
extreme dans la plupart.” The same term is, in fact, used in two distinct 
senses, in these paragraphs. 
No further proof can be necessary of the extreme vagueness and incorrect- 
* Since this paper was read, science has experienced an irreparable loss in the death of this great 
man. I will not imagine that my comments upon what I conceive to be an error in his writings will 
be misinterpreted. No one can look upon Cuvier’s labours with more sincere admiration than myself. 
2 u 2 
