Such is the course of the chyle. But the lacteal absorbents, in their progress from the intestine to the thoracic duct, pass through the small glandular bodies called the mesenteric glands (MG, p. 163), where some change, the nature of which is not at all understood, is produced upon the chyle, but which seems nevertheless to be of importance to its constitution. Where these glands are hardened and enlarged, as they often are in scrofulous children with large prominent bellies and thin bodies, nutrition is greatly impaired, although the appetite and stomachic digestion remain comparatively unaffected. The reason why the chyle is carried so far, to be poured into the current of the venous blood just before the latter reaches the right side of the heart, is on consideration not less obvious than cogent. Chyle itself is not fitted to become a constituent part of the animal frame. Before it can become so _it must be converted into blood_; and this can be effected only by exposing it to the action of the air in the air-cells of the lungs in a state of intimate mixture with the venous blood. This admixture, again, is insured by the gradual way in which the chyle advances along the thoracic duct and falls into the circulating current almost drop by drop; and it takes place just before the dark blood has finished its course, and is again subjected to complete _aëration_ in its passage through the lungs. As explained in the former volume, this aëration is so indispensable to the renovation of the old and the formation of new blood, that whenever it is rendered imperfect, either by obstructions in the lungs themselves or by the absence of a sufficiently pure air without, the result is invariably injurious to health; because the blood, being no longer properly constituted, becomes incapable of furnishing a healthy stimulus and nourishment to all the parts of the body. Hence the rapid “decline” which follows the appearance of pulmonary consumption, and other diseases affecting the structure and interrupting the functions of the lungs.