This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
The peculiarity of this subdivision is owing simply to the circumstance that, in consequence of their strong chemical affinities, they seem to be incapable of absorption into the circulation unchanged. Either their disposition to combine with salifiable bases causes them to be neutralized in the alimentary canal, and thus to lose their acid character; or a similar change in their nature takes place by union with one or more of the organic principles they meet with, as albumen for example, with which they readily unite; or they undergo decomposition; or lastly, they remain unchanged in the primae via till expelled with the feces. Indeed, this incapability of absorption unchanged, is probably essential to the prevention of poisonous effects from them; as they might very dangerously react on the blood itself through their chemical affinities. Their direct effects, therefore, as mineral acids, are confined to the alimentary canal. Various secondary effects result, to which it will be accessary to call attention in considering them severally. These may even be of a tonic character; but the acids are, nevertheless, not less distinctly characterized, as a subdivision, by the peculiarity referred to.