28 THE FOUNDATION Part I 



metabolic processes, of its power to shape the earth's surface, and its efficiency 

 in the digestive tract, in the washtub, and in the factory. Chemical reactions 

 are hastened by any agent that finely divides a solid, and this happens when 

 water divides a lump of sugar. Living depends upon chemical reactions, both 

 continual and intermittent, all of them together making up the grand process 

 of metabolism, the chemical changes in which water is a constant attendant. 

 Water conducts electricity; when salt is added it does so much more readily. 

 Thus, protoplasm is an efficient conductor since a variety of salts occurs in 

 it and especially in body fluids, the latter being similar to sea water in their 

 salt content. 



Atmospheric Gases. The gases of the atmosphere are soluble in water 

 and therefore in protoplasm. Nitrogen (No), abundant in the air (79%), is 

 always present in living cells but is chemically inactive; in pure form it does 

 not take part in metabolism although its compounds, e.g., proteins, do so. 

 On the other hand, oxygen, varyingly abundant in the atmospheric air (about 

 21%), takes an essential part in oxidation in the cells. Carbon dioxide, 

 usually 0.03 per cent in the air, is produced as a by-product of oxidation in 

 protoplasm. Although a by-product in the respiration of both plants and 

 animals, carbon dioxide is essential for photosynthesis in plants (Chap. 4), 

 and in small amounts for important functions in the respiration of animals. 



Mineral Salts. Protoplasm doubtless came into existence in sea water 

 and mineral salts must have been included in it from the beginning. It con- 

 tains a variety of salts; sodium, potassium, calcium, and magnesium are the 

 chief positively charged ions, and chloride, carbonate, phosphate, and sulfate 

 are the common negatively charged ones. Mineral salts are important in 

 maintaining the osmotic balance between protoplasm and its environment, 

 in regulating the passage of water into and out of the cell. Calcium may take 

 part in the change of protoplasm from a sol to a gel state. 



Organic Compounds. The most important difference between inorganic 

 and organic compounds is in the carbon content of the latter. This is so 

 universal that carbon is the one element with which organic chemistry deals. 

 Carbon is present in some inorganic compounds, but it is present in all or- 

 ganic ones. Virtually every organic substance will char if hot enough and 

 yield charcoal, that is, carbon. Roast pork and apples can be burned to char- 

 coal; chicken fat and chicken feathers make a lively fire. 



Protoplasm contains many organic compounds which continually shift 

 through interactions with one another. The most abundant of these are car- 

 bohydrates, lipids or fatty substances, and proteins. They constitute the main 

 part of food and are included in the discussion of foods and digestion (Chap. 

 11), but their distribution and importance make many other allusions to 

 them essential. Certain fundamental facts about them may be appropriately 

 taken up here with protoplasm. 



