Page:Popular Science Monthly Volume 18.djvu/248

236 many bad smells which, per se, though very disagreeable, have no marked poisonous action, while other very poisonous substances have comparatively little odor. Yet the disagreeable odors which accompany sewer-gas, although perhaps not always dependent upon its poisonous constituents, warn us of the presence of gases which may be intensely poisonous. Nevertheless, just as the poisonous gases may be present without any disagreeable smell, so we may have substances circulating in the blood which have the most injurious effect upon the nerve-centers, without the presence of urates in the urine.

The importance of the functions of the liver in reference to assimilation is now generally recognized, although for a long time this, the largest gland in the body, was considered to have no other office than simply to secrete bile. Although the bile is useful in digestion it is not of primary importance in this process; but its proper secretion is probably associated very closely with the assimilative functions of the liver, and if the biliary secretion does not take place properly we can hardly expect the assimilation to be perfect.

The greatest care appears to have been taken in the construction of the liver to prevent the bile from coming in contact with the blood, the ultimate radicals of the bile-ducts or biliary capillaries being placed as far from the blood capillaries as the structure of the liver will allow. Notwithstanding this care, the distance between the blood and the bile capillaries is small, though it is sufficient, under ordinary circumstances, to prevent the absorption of bile into the blood. But whenever an obstruction takes place to the exit of bile, and the presence of bile in the biliary capillaries increases, an absorption of this secretion occurs. Bile is secreted under very low pressure, and a very slight increase in this is sufficient to cause reabsorption. Such an increase as would not materially affect the secretion of other glands, such as the salivary gland, is sufficient to prevent the exit of bile through the biliary ducts, and cause its reabsorption into the blood. The excretion of bile is greatly aided by the pressure which is exerted upon it by the movements of the diaphragm during respiration, and indeed so low is the pressure under which the bile is secreted that, but for the assistance given by the respiratory movement, it would just barely find its way into the duodenum. Although we are accustomed to say "as bitter as gall," according to my own observations fresh human bile is not bitter. When it is thrown up in consequence of indigestion it is intensely bitter. On one occasion, when making experiments with digitalis, I had taken in the course of two days one grain of the pure alkaloid, and brought on symptoms of poisoning, with intense vomiting. During this I brought up a quantity of bile of a golden-yellow color, and without the least trace of bitterness. This circumstance struck me as being so peculiar that in my published results I hesitated to call it bile, although I did not