236 
Dr. Kidd on the 
that “ the blood being incapable of going in search of the 
air, the air goes in search of it,'' will still remain inviolate. 
If it should be argued that the tracheae are not found 
charged with blood after the death of the animal, it may be 
answered, that neither are the arteries in the higher orders 
of animals found charged with blood after their death. How- 
ever, I have actually seen some of the ramifications of those 
tracheae which are connected with the caeca distended with a 
fluid of the same colour as that found in those organs ; and 
though I have only witnessed this fact in two instances ; yet 
such a fact, even singly taken, must be allowed to be of con- 
siderable importance. 
Of one thing I am certain, that, after careful observation, 
I have never found the abdominal viscera, I will not say 
bathed,'as some authors of credit have expressed themselves, 
in the nutrient fluid which is supposed to have transuded 
through the coats of the intestines ; but I have not even 
found them lubricated by a greater proportion of moisture 
than lubricates the intestines of the higher classes of ani- 
mals. 
There is another difficulty which occurs to the hypothesis 
of the transudation of the chyle through the coats of the in- 
testines ; for, if the blood be conveyed to the several parts 
by previous general diffusion through the interior of the 
body, and then by absortion into the substance of particular 
organs, as the hepatic tubes, the vesiculae seminales and the 
ovaries ; how does it happen that the bile, for instance, does 
not transude through the coats of the same vessels, the pores 
of which have admitted the blood from which it has been 
formed It may be answered, that the alteration which the 
