About the middle of this century there arose a new sect of chemical philosophers, somewhat better informed than the last. They imagined that most diseases depended on the predominance in the blood of _acid_ or _alkalic humours_, and that each of these conditions should be counteracted by a direct chemical antidote. They supposed also that the various secretions were the products of _fermentations_ in the blood which took place in the neighbourhood of the glandular organs. (_Vide_ Eliminatives.) In some of their ideas there was much that was reasonable; but it must be confessed that they were rather imaginative than argumentative, and, knowing really but little of the principles of that science on which their system was ostensibly based, they were ill-qualified to contend with their opponents of the mathematical school, who at least understood their own position. Foremost among these new chemical philosophers was Raymond Vieussens, who was severely censured by Dr. Pitcairn for having asserted that he had found an acid in human blood.[12] Vieussens was one of the earliest of the sect, which afterwards numbered many followers.
There is very little that is tangible to be discovered in these old chemical theories of the action of medicines; and it is not to be wondered at that most of them have faded away before the advance of science, and particularly before that wonderful development of the science of chemistry, which has distinguished the end of the last, and the first half of the present century.
We have seen that some of the early writers made great account of the affinities of acids and alkalies. So also a chemical explanation of the action of these remedies is generally adopted by writers at the present day. It is known that they have powerful tendencies to combine with each other, and it is supposed that these affinities are manifested even in the living blood.
Schultz attempts a further chemical explanation of their action in some diseases, particularly inflammations. He says that both affect the condition of the blood; but that acids tend to dissolve and destroy the corpuscles, wherefore he terms them _Hæmatolytica Physoda_; and alkalies prevent the coagulation of the fibrine of the plasma, for which reason he calls them _Hæmatolytica Plasmatoda_.