THE DISEASES OF CATTLE. 53 



osseous system of birds of high flight. We also know that in 

 insects, which, like birds, have need of great specific lightness, 

 .here exists plenty of air, brought by the trachea, and after- 

 wards distributed through the different parts of the animal, to 

 place it in relation with the molecules designed for its as- 

 similation. 



" 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 Generale, 



'' 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 tissues 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 mem- 

 branes. It is thus that we account for peritoneal tympanitis 

 when there exists no mechanical lesion ; viz., through the effect 

 of physiological 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 

 sequel of the softening of the tubercles in communication 

 with the bronchii. In this last state, the air proceedhig from 

 5* 



