34 



IRRITABILITY. 



irritability ; whilst, on the other hand, he 

 makes statements which appear to me at va- 

 riance with this very opinion. In the Ana- 

 tomie Comparee (tome i. p. 49,) this cele- 

 brated writer observes, " Les experiences 

 modernes ont montre qu'un des principanx 

 usages de la respiration est de ranimer la force 

 musculaire, en rendant a la fibre son irrita- 

 bilite epuisee." See also tome iv. p. 301. 

 Similar observations are made in M. Cuvier's 

 more recent work, the Regne Animal : " C'est 

 de la respiration que les fibres musculaires 

 tirent 1'energie de leur irritabilite," (tome i. 

 p. 57, 2me edit.) " C'est la respiration qui 

 donne au sang sa chaleur, et a la fibre la sus- 

 ceptibilite pour 1'irritation nerveuse," (tome li. 

 p. 1.) On the other hand, speaking of the 

 mollusca, (tomeiii. p. 3,) M. Cuvier observes 

 of those animals of low respiration, " L'irri- 

 tabilite 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 incorrectness of the 

 prevailing notions and expressions of physio- 

 logists in regard to this subject. All this will 

 appear still more extraordinary, when the 

 law, that the quantity of respiration and the 

 degree of the irritability are, in fact, inverse 

 throughout all the series, stages, and states of 

 animated being, is clearly established. 



It is well known that the irritability of the 

 heart and of the muscular fibre in general is 

 greater in the mammalia than in birds, and in 

 reptiles and amphibia than in the mammalia, 

 whether we judge of it by the force and dura- 

 tion of the beat of the heart, exposed to the 

 stimulus of the atmospheric air, or by the con- 

 tractions of the other parts of the muscular 

 system. Now this is precisely the order of the 

 quantity of respiration in these animals, as 

 ascertained by the pneumatomer, inverted. It 

 is essential, in accurately determining the ques- 

 tion of the irritability of the muscular fibre, to 

 compare animals of the same class inter se ; 

 birds and the mammalia, reptiles and amphibia, 

 fishes, the mollusca, &c. must be compared 

 with each other, both generically and specifi- 

 cally. It is especially necessary to compare 

 the warm-blooded, the cold-blooded, the air- 

 breathers, and the water-breathers, in this man- 

 ner. However the different classes may differ 

 from each other, there are differences in some 

 of the species of the same class, and especially 

 that of fishes, scarcely less remarkable. 



Great differences in the duration of the beat 

 of the heart are observed in foetal, early, and 

 adult states of the higher animals; this dura- 

 tion being greater in the first, and least in the 

 last of these conditions. The order of the 

 quantity of respiration is inverse. 



The law of the irritability being inversely as 

 the respiration, obtains even in the two sides of 

 the heart itself, in the higher classes of animals. 

 The beat of the heart removed from the body 

 does not cease at the same time in the wall of 

 all its cavities, or of its two sides : but, as 

 Harvey observes, " primus desinit pulsare 

 sinister ventriculus ; deinde ejus auricula; de- 



mum dexter ventriculus ; ultimo (quod etiara 

 notavit Galenus) reliquis omnibus cessantibus 

 et mortuis, pulsat usque dextra auricula."* 



Even in this case the irritability is greatest in 

 the part in which the respiration is least. 



It was shown by Hook, in the early days of 

 the Royal Society,f that if, the respiration 

 being suspended, an animal appeared to be 

 dying, the beat of the heart and the signs of 

 life were speedily restored, on performing arti- 

 ficial respiration, or even by forcing air through 

 the trachea, bronchia, and pulmonary air-cells 

 and allowing it to escape through incisions 

 made through the pleura. 



It was, in the next place, clearly shown by 

 Goodwyn, in one of the most beautiful spe- 

 cimens of physiological inquiry in any lan- 

 guage,]: that in suspended respiration, it is the 

 left side of the heart which first ceases to 

 contract, the right side still continuing its 

 function for several minutes, until the supply 

 of blood may be supposed to fail. 



The facts detailed by Harvey had shown that 

 the left side of the heart was endued with less 

 irritability than the right ; the experiment of 

 Hook, that respiration restored the action of 

 the heart, if it had previously ceased ; that of 

 Goodwyn, that this cessation and restoration 

 of functions were observed in the left side of 

 the heart. It was obvious, on the other hand, 

 that the respiration belongs, as it were, to the 

 left side of the heart. 



It appears plainly deducible from these facts, 

 that in circumstances and structures the most 

 similar, the respiration is accurately inversely 

 as the irritability. 



For the sake of a comparison with the hy- 

 bernating animal, the object of which will be 

 explained hereafter, I thought it right to repeat 

 this experiment. 



Before I proceed to detail the result, I may 

 just describe an easy method of performing 

 that part of it which consists of artificial respi- 

 ration. A quill is firmly fixed in the divided 

 trachea : a small hole is then cut into that part 

 of the quill which is external; Read's syringe 

 is then adapted to the other end of the quill. 

 At each motion of the piston downwards, the 

 lungs are distended ; whilst the piston is raised, 

 the air escapes through the opening in the quill, 

 producing expiration. The experiment, there- 

 fore, only requires the common action of the 

 syringe. 



The experiment itself answered my expecta- 

 tion. During the cessation of respiration, the 

 left ventricle ceased to beat, the right ventricle 

 retaining its function ; on renewing its respira- 

 tion, the left ventricle resumed its beat. It 

 appears from this experiment, that from want 

 of a degree of irritability equal to that of the 

 right ventricle, and its own proper stimulus of 

 arterial blood, the left ventricle ceased its con- 

 tractions. The function of the right ventricle 



* Opera Omnia, Collegio Medicorum Londinensi 

 edita, 1766, p. 28. 



t Phil. Trans, vol. ii. 



j On the Connexion of Life with Respiration : 

 London, 1788, p. 72, 82 note. 



