328 
DR. MARSHALL HALL ON THE INVERSE RATIO 
ness of the prevailing notions and expressions of physiologists 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 the 
amphibia than in the mammalia, whether we judge of it by the force and 
duration of the beat of the heart, exposed to the stimulus of the atmospheric 
air, or by the contractions 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 pneumatometer, inverted. It is essential, in accurately 
determining the question of the irritability of the muscular fibre, to com- 
pare animals of the same class inter se; birds and the mammalia, reptiles 
and the amphibia, fishes, the mollusca, &c. must be compared with each other, 
both generically and specifically. It is especially necessary to compare the 
warm-blooded, the cold-blooded, the air-breathers, and the water-breathers, 
in this manner. 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 
the foetal, early, and adult states of the higher animals ; this duration being 
greatest 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 walls 
of all its cavities, or of its two sides : but, as Harvey observes, “ primus de- 
sinit pulsare sinister ventriculus ; deinde ejus auricula; demum dexter ven- 
triculus ; ultimo (quod etiam 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 respira- 
tion is least. 
* Opera Omnia, Collegio Medicorum Londinensi edita, 1766, p. 28. 
