154 



ANATOMY AND PHYSIOLOGY OF THE HORSE. 



The absorbents of the lungs are large and 

 numerous, particularly the deep-seated : and 

 of the superficial, we may often succeed in 

 injecting considerable numbers, by intro- 

 ducing a quicksilver-pipe under the pleura 

 pulmonalis. They all pass through the 

 absorbent glands situated around the roots 

 of the bronchial tubes. 



Parenchyma. — The connecting medium 

 of the various constituent parts of these 

 organs, or, as it is termed, their parenchyma^ 

 appears to consist of little else than cellular 

 tissue, without any intermixture of adipose 

 matter : it admits of the free diffusion of 

 any fluid that may be extravasated into it 

 — of air that may have escaped from the 

 air-cells, or of serous fluid poured out when 

 the lungs become anasarcous ; but, as was 

 observed before, there is no intercommuni- 

 cation between it and the cells or vessels, as 

 long as the organs preserve their integrity 

 of structure. 



Specific Gravity. — The lungs, when 

 healthy, are exceeding light in comparison 

 to their volume ; so that, if they be immersed 

 in water, unlike most other parts, they will 

 float upon the surface, — a fact familiar to 

 every one who has seen the liver and lights 

 of an animal thrown into a pail of water 

 to be washed : indeed, the name of lights 

 itself seem to have been given to them from 

 this very property. If the foetal lungs, how- 

 ever, be so ti'eated, they will instantly sink 

 to the bottom of the vessel : and this ex- 

 I^rimental result at once shows why those 

 ol an animal that has once breathed should 

 swim ; for, in the one instance they contain 



air, in the other they are wholly free from 

 it. They are not to be regarded as respi- 

 ratory organs in the foetus. It is evident, 

 therefore, that the lungs owe their property 

 of lightness to the air they contain ; and, as 

 a further proof of it, if that air be by any 

 means absorbed or pressed from them, and 

 their bulk diminished by collapse of the 

 air-cells, like other viscera, they will prove 

 heavier than an equal volume of water: 

 hence it is that the lungs of a horse that 

 has died of hydrothorax, even though they 

 be sound, are of a greater specific gravity 

 than those of one in health. It occasionally 

 happens, however, that these viscera evince, 

 in this particular, the properties of airless 

 lung, while their natural volume and general 

 appearance remain the same : there must be 

 present interstitial deposition. 



BRONCHIAL GLANDS. 



Small, oval-shaped, glandular-looking 

 bodies, situated about the roots of the lungs, 

 adhering more particularly to the bottom 

 of the trachea and the bronchial tubes. 

 They exhibit a dirty French gray hue, inter- 

 spersed with dark blueish spots, and are 

 about the volume (though this varies much) 

 of a tick-bean. For a long time the nature 

 of these bodies remained obscure : of late, 

 skilful injections have clearly shown them 

 to be absorbent glands. They possess their 

 capsules, and, when cut open, exhibit a cel- 

 lular structure. They contain a dark fluid, 

 which will soil anything it touches ; whose 

 principal ingredient chemists have found to 

 be carbon. 



