ON THE MORBID STATES DENOMINATED PNEUMATOSES. 107 
M . de Blainville assures us that the swimming-bladder has no 
communication with the buccal cavity. He has never been 
able to empty it through this passage, nor to force the gas out 
of it through the respiratory channels. Indeed, the analysis 
made of it by Messrs. Rumboldt, Provencal, and Delaroche, has 
shewn that it is not directly furnished by the air of respiration, 
but must be the product of a particular secretion. 
The feathers of birds are, likewise, another example of air 
reservoirs having no communication with the respiratory pas- 
sages; the air appearing to be introduced into them through 
absorption, at the period when the gelatinous matters disappear 
which up to that time had filled the tubes. 
We know that the air of respiration gains admission into the 
osseous system of birds of high flight. We also know that in 
insects, which, like birds, have need of great specific lightness, 
there exists plenty of air, brought by the trachea, and afterwards 
distributed through the different parts of the animal, to place 
it in relation with the molecules designed for its assimilation. 
Among fish, shell-fish enjoy the faculty, which to them proves 
a source of health, of filling their stomachs with air, and so of 
considerably augmenting the volume of their body, and, through 
an extension of their skin, facilitating the erection of the scales 
by which it is covered, and which remain depressed so long as 
the skin continues in inaction. It is likewise the atmospheric 
air which enables that frolicsome animal known by the name of 
dolphin to render himself light enough to swim upon the surface 
of the sea (Blainville’s Physiologie Ginirale). 
Not even vegetables are without reservoirs containing air. 
Chemists have demonstrated that it is the fluid found in certain 
plants of the leguminous family, that fills and swells the peri- 
carp at the period of maturity; and Gaspard has assured him- 
self, in opening under water many seeds of the same family, 
regarded by physicians as full of wind, that they contain in 
their tissue a large quantity of atmospheric air. 
In regard to collections of gas within the serous cavities, such 
as the peritoneum, the pleura, and even the pericardium, they 
are attributed, and with reason, to two different sources, — to the 
atmospheric air, and to an exhalation from these membranes. 
It is thus that we account for peritoneal tympanitis when there 
exists no mechanical lesion, viz. through the effect of physiolo- 
gical operation ; but in a much greater number of cases they 
proceed from rupture of the stomach or intestine. 
Pneumatosis of the pleura depends, most commonly, upon 
these two latter circumstances ; either proceeding from rupture 
of some air-cell near the surface, as in the case of emphysema ; 
or else from the perforation of the pulmonary pleura, as the 
