330 
DR. MARSHALL HALL ON THE INVERSE RATIO 
respiration, the left ventricle ceased to beat, the right ventricle retaining its 
function ; on renewing the respiration, 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 contractions. The function of the right ventricle 
must soon cease in consequence, from want of a supply of blood. 
These facts prove that arterial blood is the necessary stimulus of the left 
side of the heart, its irritability being low ; but that venous blood is a sufficient 
stimulus of the right, from its higher irritability : the phenomena plainly flow 
from the law, that the quantity of respiration and the degree of irritability, 
observe an inverse ratio to each other, and from the facts on which that law is 
founded. In this double sense, besides that of distinct cavities, the mammalia 
have, therefore, two hearts ; and as the highly aerated blood of the left is the 
peculiar property of birds and the mammalia, so the highly irritable fibre of the 
right may be compared to that of the heart of reptiles and the fishes. 
Except for the objection to new terms, the left side of the heart might be 
termed arterio-contractile, and the right veno-contractile ; the first being stimu- 
lated by arterial, the second by venous blood. 
It is quite obvious that the heart will bear a suspended respiration better, 
the more nearly its irritability approaches to that which may be designated 
veno-contractile. The power of bearing a suspended respiration thus becomes 
a measure of the irritability . It is expressed, numerically indeed, by the length 
of time during which the animal can support a suspended respiration ; a con- 
clusion of the highest degree of importance in the present inquiry. 
Birds die almost instantly on being submerged in water ; the mammalia 
survive about three minutes, the reptiles and the batrachia a much greater 
length of time. 
The unborn foetus, the young animal born with the foramen ovale open, the 
reptile, the mollusca, having all a state of the heart approaching to the veno- 
contractile, bear a long-continued suspension of the respiration, compared with 
the mature animal of the higher classes. 
But the most remarkable fact dcducible from this reasoning is the follow- 
ing: if such a case existed as that of the left side of the heart being nearly or 
absolutely veno-contractile, such an animal would bear the indefinite suspen- 
