Properties and Activities of Living Protoplasm 89 



(NH2). Hence they are amphoteric (am'foterik) (Gr. amphotere, in 

 both ways), which is probably important in regulating the proper acid- 

 base relationship in living protoplasm. 



The large size of their molecules causes proteins to assume colloidal 

 characteristics in water, which explains the colloidal nature of proto- 

 plasm. Proteins contribute the structural components of protoplasm, as 

 well as important constituents of enzymes and certain hormones, in addi- 

 tion to supplying energy and heat. They assist greatly in growth and 

 repair. Animal protoplasms, in general, seem to be able to manufacture 

 only a few types of amino acids from raw materials, while plants can 

 synthesize many of them from simpler substances. In general, animals 

 are dependent, directly or indirectly, on plants for most of them. When 

 proteins are digested, they are broken up into amino acids before they 

 can be absorbed by the blood, which carries them to various parts of the 

 body where they are made into new proteins. The digestion of proteins 

 releases energy which was required to hold their components together. 

 Examples of proteins with their chemical formulas are ( 1 ) albumin of 

 the white of e^g (C239H389O78N58S2) and (2) zein of corn (CtsbHiisi- 



^208Ni84S3) . 



D. Mineral (Inorganic) Salts 



In spite of the fact that mineral salts are not present in great quan- 

 tities, they are nevertheless of great importance in maintaining the nor- 

 mal activities and physiologic equilibrium of living protoplasm. Chemi- 

 cal analysis of body fluids reveals that the quantity and kinds of salts 

 in them greatly resemble the concentrations of the mineral salts of sea 

 water from which the first protoplasm is thought to have originated. 

 The different salts in ocean water are sodium and magnesium chlorides, 

 magnesium, calcium, and potassium sulfates, and calcium carbonate, in 

 addition to minute quantities of other salts. When these salts dissociate 

 in water (ionize), the sodium, magnesium, calcium, and potassium con- 

 tribute positively charged ions, and the chlorine, sulfates, and carbonates 

 contribute most of the negatively charged ions. These positive and 

 negative ions are probably associated with certain electrical phenomena 

 of protoplasm. 



Normally, the concentration of the various salts in body fluids is quite 

 constant, because any appreciable deviation will be followed by im- 

 paired functions, or possibly death in extreme cases. Calcium salts are 

 important in the building of bones and the coagulation of blood. A 

 sufficient decrease in the calcium ions in the blood may result in con- 



