42 
Dr. Carson on the 
it, and fully adequate to all the important offices which I 
have ventured to assign to it. From a defect in the apparatus, 
the extent of the power in question could not be ascertained 
in the lungs of oxen and animals of their size; but it was 
proved to exceed, considerably, the force necessary to sup- 
port a column of water of a foot and a half in height above 
its level. In calves, sheep, and in large dogs, the resiliency 
of the lungs was found to be balanced by a column of water 
varying in height from one foot to a foot and a half, and in 
rabbits and cats, by a column of water varying in height from 
six to ten inches. 
The method by which nature has contrived to apply this 
powerful engine to the heart and diaphragm, I have attempted 
to explain at length in the treatise already mentioned. In a 
preceding part of this paper, however, I have stated, that 
during the life of the animal, and after death, until an opening 
shall have been made into the cavity of the chest, the dia- 
phragm assumes the form of a cone, and that the causes of 
this phenomenon would be afterwards pointed out. The 
brief explanation which is now to be given of this appearance, 
will afford, at the same time, a perspicuous view of some of 
the important purposes to which, in my opinion, nature has 
turned the elasticity of the lungs. 
While the chest is in a sound state, a balance of atmos- 
pherical pressure ponderates against the external surface of 
its walls ; or these are pressed inwards more than they are 
pressed outwards by a given weight. The shell of the chest 
possesses sufficient stability to resist this pressure without 
changing in any considerable degree its form and capacity at 
all parts, except at the base, or diaphragm ; which being 
