664 MR. youatt’s veterinary lectures. 
of those anatomists, whose experiments on the living animal da 
no credit to their humanity, have given us most singular proof af 
the insensibility, not only of these serous membranes, but of the 
organs which they invest. Bichat frequently examined the spleen 
of dogs. He detached it from some of its adhesions, and left it 
protruding from the wound in the abdomen “to study the phe¬ 
nomena ; 77 and he saw “ themselves tearing off that organ, and 
though in a state perfectly calm, eating it, and thus feeding upon 
their own substance. 7 ’ In some experiments, in which part of 
their intestines were left out, he saw them, as soon as they had the 
opportunity, tear them without any visible pain. 
Except under Disease. —Although it may be advantageous 
that these important organs shall be thus devoid of sensibility 
when in health, in order that we may be unconscious of their 
action and motion, and thus they may be rendered perfectly in¬ 
dependent of the will, yet it is equally needful that, by the feel¬ 
ing of pain, we should be warned of the existence of any danger¬ 
ous disease : and thence it happens that this membrane, and also 
the organ which it invests, acquire under inflammation the highest 
degree of sensibility. The countenance of the horse labouring 
under pleurisy or pneumonia, will sufficiently indicate a state of 
suffering; and the spasmed bend of his neck, and his long and 
anxious and intense gaze upon his side, tell us that that suffering 
is extreme. 
Yet not under every Disease. —Nature, however, is wise and 
benevolent even here. It is not of every morbid affection, or 
morbid change, that the animal is conscious. If a mucous mem¬ 
brane is diseased, he is rendered painfully aware of that, for 
neither respiration nor digestion could be perfectly carried on 
while there was any considerable lesion of it; nay, the animal 
often expresses a great degree of pain, plainly referrible to these 
membranes, and yet on examination after death they exhibit little 
or no morbid change : but, on the other hand, we find tubercles 
in the parenchyma of the lungs, or induration or hepatization of 
their substance, or extensive adhesions, of which there were few 
or no indications during life. 
The adherent Surface of the Pleura .—In some few cases (and 
the thorax furnishes us with one) the pleura is isolated on both 
sides. It is so in the mediastinum, and then both sides present 
the same polished glistening appearance; but a serous membrane 
is generally an investing one, and then it has a very different 
surface internally, namely, a roughened flocculent one, by means 
of which it adheres so closely to the part beneath, as to be 
scarcely separated by the most careful dissection. The pleura 
adheres intimately to the ribs and to the substance of the lungs; 
