Page:Popular Science Monthly Volume 66.djvu/157

Rh from the beaten course, and turning out year after year a definite line of products for the specific purpose in view. Why is it that the epithelial cells of the salivary glands always manufacture mucinogen and ptyalin; the gastric gland cells pepsinogen, renninogen and hydrochloric acid; the cells of the pancreas trypsinogen and steapsin; the hepatic cells bilirubin, biliverdin and the specific bile acids; the cells of the thyroid iodothyrin, and the cells of the adrenals epinephrin? Essentially the same blood and lymph bathe all these cells with a like nutritive pabulum, and yet each group of cells performs its own line of work, never going astray, in health, and never even temporarily producing a product which rightfully belongs to the other class of cells. Are we to suppose that all these varied products are manufactured from the same cell protoplasm, from a common stock, that each one owes its origin to some particular force controlled by extra-cellular influences, each group of cells' being made to manufacture a given product out of the same mother substance? Or, on the other hand, are we to assume that each group of cells, as it is developed, has as a birthright the quality of producing from its particular protoplasm a certain line of products, simply because of the peculiar chemical nature or constitution of that protoplasm?

In other words, do all the intricacies of cellular activity depend primarily upon the character of the anabolic processes by which that protoplasm is built up out of the food materials by which the cells are nourished? It may be just as difficult to explain why and how the cells are able to manufacture a specific protoplasm out of a common pabulum, but the main problem which confronts us is surely capable of being solved. We need to know how far the primary cell constituents of different groups of cells, of the different organs and tissues are similar or unlike each other. If it is shown that the primary cell constituents differ for each glandular organ and tissue, that each group of individualized cells has a protoplasm characterized by some specific feature, then we shall have reason to believe that the anabolic processes are as much, if not more, responsible for individuality of function than the katabolic processes. We may conceive of all protoplasm being built, so to speak, on a certain general plan of structure, but with side chains of varying nature, and that these side chains determine in a measure the character of the katabolic or alteration products that result from the natural activity of the cell protoplasm. In other words, if this conception be true, it is the chemical constitution of the cell protoplasm that is primarily responsible for the character of the changes that take place in all active tissues and organs. The extent of oxygenation as influenced by the circulating blood, the direct and indirect influence of various nerve fibers, etc., may all act as modifying agents, but only to the degree of accelerating or inhibiting the rhythmical process which