834. Taking together the whole of the apparatus of absorption, the specific office performed by its several parts seems to be as follows:— 835. 1. It is established that the lacteals absorb chyle, and that they refuse to take up almost every other substance which can be presented to them. Experimentalists are uniform in stating that however various the substances introduced into the stomach, it is exceedingly rare to find in the lacteals anything but chyle. These vessels appear to be endowed with a peculiar sensibility, derived from the nervous system, by which they are rendered capable of exerting an elective power, readily absorbing some substances and absolutely rejecting others. 836. 2. The lymphatics absorb a far greater variety of substances than the lacteals, but not all substances indiscriminately; chiefly organized matter in a certain stage of purification; particles passing through successive processes of refinement (707). 837. 3. The blood-vessels, and more especially the capillary veins, appear to absorb indiscriminately all substances, however heterogeneous their nature, which are dissolved or dissolvable in the fluids presented to them. 838. 4. The absorbent glands appear by various modes, either by removing superfluous and noxious matters, or by the addition of secreted substances possessing assimilative properties, to approximate the fluid which flows through them more and more closely to the nature of the blood. Fatal effects result from the artificial infusion of minute portions even of mild substances into the blood. Hence the extended and winding course which Nature causes the new matter formed from the food to undergo, even after its elaboration in the digestive apparatus, in order that, before it is allowed to mingle with the blood, its perfect purification and assimilation may be secured.