394 PROFESSOR ALISON’S DEFENCE 
salivary glands, of the testes, even of the liver, of which the organisation is the 
most uniform, and likewise of the kidneys.” “It would be interesting also,” he 
adds, “to compare the secreting organs with their secreted fluids, and observe 
whether the organs that have a similar structure afford similar products. But 
experience will sanction no such theory. Nothing, for example, can be more 
various than the matter furnished by ‘ crypts’ in different animals, from a simple 
mucus to the most odoriferous compounds.” ‘The simplest secreting organs,” he 
observes elsewhere, “are in insects, where they are merely tubes which float in the 
general nourishing fluid, which is in contact with their outer surface, while their 
inner surface contains the secreted fluid. Secretion there can be only a kind of 
filtration ; but how different from that which can take place where there is no 
life, through ‘an inorganic solid!’ ” (Lecons sur ? Anat. Comp. Lect. xxx., Art. 1.) 
But farther, not only is the complex vascular structure and the varying pres- 
sure from contracting solids, which was regarded by Murray as the main cause 
of the formation of new compounds out of the blood, shewn by the examination 
of other animals, to be quite unnecessary for that purpose; but we now know, 
that where these conditions exist, that formation is never effected—the most com- 
pound fluids of the animal economy, which appear in the different glands, being 
really not formed there, but in the course of circulation, and appearing in the 
blood or in other parts of the body when the organs where they usually appear 
have been extirpated, or rendered useless by disease; that is, when the cause to 
which their origin is here ascribed has been absolutely withdrawn. 
The mere selection and attraction out of the blood at different places, of dif- 
ferent compounds already existing and circulating in it, is certainly the chief, and, 
according to many, and particularly according to Dr Dauseny himself, the sole 
office, performed by any parts of animals by which any new organic products are 
exhibited; and the office of forming those organic compounds, the origin of which 
is the great chemical change effected by living beings, is performed by no organ 
capable of exerting a varying power of contraction and pressure, but simply by 
the cells of vegetables, where the fluid introduced from without is usually not con- 
veyed in vessels at all, and is clearly not subjected to any such pressure from 
contracting solids, as is exerted on the blood in most animals ; nor to any such 
peculiar cause of movement as can be ascribed to the living property of contrac- 
tility, the only one which Dr Davubeny admits to be strictly vital. 
I have formerly stated, and notwithstanding the opposition of Dr DauBeny 
and others, still think, that the judgment of various authors on the respective 
offices of vegetables and animals as to vital attinities,—the supposition that no 
organic compound can be formed in animals, and that their office is merely the 
selection and appropriation of the compounds formed in vegetables, and after- 
wards the destructive assimilation by which these are restored, through the excre- 
tions, to the inorganic world, is too hasty. It appears from the experiments of 

