28 HUMAN PHYSIOLOGY. 



as protoplasm is the seat of constructive and destructive processes, it is not 

 easy to determine whether the products of analysis are crude food constit- 

 uents or cleavage or disintegration products. Nevertheless, chemic investi- 

 gations have shown that even in the living condition protoplasm is a highly 

 complex compound the resultant of the intimate union of many different 

 substances. About seventy-five per cent, of protoplasm consists of water 

 and twenty-five per cent, of solids, of which the more important compounds 

 are various nucleo-proteins (characterized by their large percentage of 

 phosphorus), globulins, traces of lecithin, cholesterin, and frequently fat 

 and carbohydrates. Inorganic salts, especially the potassium, sodium, 

 and calcium chlorids and phosphates, are almost invariable and essential 

 constituents. 



MANIFESTATIONS OF CELL LIFE. 



Growth, the Maintenance of Nutrition and Reproduction. All cells 

 exhibit the three fundamental properties of life viz., growth, the maintenance 

 of nutrition and reproduction. All cells when newly reproduced are ex- 

 tremely small, but by the absorption of nutritive material from their sur- 

 rounding medium, they gradually grow until they attain their mature size. 

 This is accomplished by the power which living material possesses of trans- 

 forming, vitalizing, and organizing crude nutritive material, through a series 

 of upward changes, into material similar to itself. To all these changes the 

 term assimilation, or anabolism, has been given. Some of the absorbed 

 material, in all probability, never becomes an integral part of the living 

 bioplasm, but undergoes disruption and oxidation, giving rise at once to heat. 

 Coincident with the assimilative processes, a series of disintegrative processes 

 is constantly taking place, whereby the living material is reduced, through 

 a series of downward chemic changes, to simpler compounds, such as water, 

 carbon dioxid, urea, etc. To all these downward changes the term dis- 

 similation, or katabolism, has been given. As a result, also, of these various 

 changes, the protoplasm gives rise to the production of material of an entirely 

 different character, such as globules of fat, granules of glycogen, mutigen, 

 digestive ferments, etc. The sum total of all changes which go on in the cell, 

 both assimilative and dissimilative, are embraced under the general term 

 nutrition, or metabolism. Every cell presents in its nutritive activities an 

 epitome of the nutritive activities of the body as a whole. 



Physiologic Properties of Protoplasm. All living protoplasm pos- 

 sesses properties which serve to distinguish and characterize it viz., irrita- 

 bility, conductivity, and motility. 



Irritability, or the power of reacting in a definite manner to some form of 



