It is certain that in the case of the submaxillary gland secretion is not the direct result of increased blood-pressure. It is not a case of filtration from the blood through certain membranes and cells into the salivary duct. Atropin (belladonna) dilates the bloodvessels, increasing blood-pressure, but it stops secretion. After belladonna-poisoning, the mouth, like the skin, is hot and dry. Other drugs there are which provoke a certain amount of secretion, even after the bloodvessels going to the gland have been tied. It is possible, by stimulating the chorda tympani, to obtain a pressure in the fluid in the duct very much greater than that in the bloodvessels which supply the gland. Here we have clear proof that secretion is not filtration. Filtration is the passage of fluid through a filter-bed from a higher to a lower pressure. In filtration, moreover, soluble diffusible salts accompany the water. The saliva contains only half as much of these diffusible salts as the blood. Therefore the gland tissue stops half the salts. Secretion is an active process carried out by the gland-cells, under the influence of nerves, in opposition to the laws of filtration. The gland-cells determine how much water shall pass through them and what percentage of salts shall accompany the water. How does a gland-cell make the substance which it secretes? There is no reason for supposing that the ptyalin or the mucus which the salivary glands secrete is present in the blood, either ready formed, or, as it were, half formed, in combinations which can be easily broken up. All the evidence obtainable points to the conclusion that the gland-cells take out of the lymph proteid materials from which they manufacture the peculiar substances which they secrete. During rest, granules accumulate in the cells. During activity they disappear. It has been shown in the case of the gastric glands that these granules consist of the special ferment which the gland secretes, in an inactive form. It may be that it is combined with a substance which prevents it from exerting its digestive action on the cells within which it is made; damped, as gunpowder is damped during transit. Or it may be that it is not a finished ferment; it may need a further addition to its molecule. During activity, while the granules disappear, proteins accumulate at the bases of the cells, giving to a tube of gland-cells the appearance of a peripheral non-granular zone. This proteid substance must have come from the lymph, and the inference seems inevitable that the cells have taken into their protoplasm a supply of material which will serve for the manufacture of additional granules. Each gland-cell is therefore an independent unit. By its own activity it takes up materials from the lymph, out of which it manufactures its own special products. It stores its products until they are wanted. Then by its own activity it extrudes them into the lumen of the gland-tube. It