28 GENERAL ZOOLOGY 



from a scientific point of view, and, of course, does not ex- 

 plain the origin of life. 



PHYSICAL BASIS OF LIFE 



If we cannot explain the origin of life we may at least look 

 into the nature of living matter. The name, protoplasm, 

 has been given to the complex mixture of chemical com- 

 pounds which makes up the living substance. It is a trans- 

 parent semi-fluid material, somewhat like the white of an 

 egg. At one time there was considerable dispute in regard 

 to the structure of protoplasm. One school maintained 

 that there were granules which were all-important; others, 

 that little fibers were the living elements; a third group 

 that little bubbles were the necessary feature. Modern 

 investigation has shown, however, that none of these things 

 are of prime importance. The same bit of protoplasm may 

 at different times be granular, or reticular, or alveolar. It 

 is more or less clear and jelly-like; it shows spontaneous 

 internal movements; it is alive these are the only constant 

 features to be seen even through the best microscopes. 



Protoplasm is somewhat variable in its composition be- 

 cause it is unstable chemically, and is continually chang- 

 ing. Nevertheless, it shows a general similarity of struc- 

 ture and elemental composition in all plants and animals. 

 It is made up of twelve of the eighty-odd known chemical 

 elements. These are : 



Carbon, oxygen, hydrogen, nitrogen, sulphur 99 percent. 



Chlorine, phosphorus, potassium, sodium, magnesium, 

 calcium, iron 1 per cent. 



Protoplasm shows some chemical peculiarities which are 

 noteworthy. (1) The element carbon has remarkable 

 ability to form extremely complex systems of combinations 

 with other elements and its compounds are most important 

 (Fig. 19). (2) Protoplasm is very labile, or unstable. 

 Living substance may readily incorporate a little more 

 water (or other compound) or lose a little as the necessity 



