THE PHENOMENA OF LIFE. 3 



history of its own. Each cell goes through the same cycle of changes as 

 the whole organism, though doubtless in a much shorter time. Begin- 

 ning with its origin from some pre-existing cell, it grows, produces other 

 cells, and finally dies. It is true that several lower forms of life consist 

 of non-nucleated protoplasm, but the above definition holds good for all 

 the higher plants and animals. 



Hence a summary of the manifestations of cell life is really an ac- 

 count of the vital activities of protoplasm. 



Protoplasm. Physically, protoplasm is viscid, varying from a 

 semi-fluid to a strongly coherent consistency. Chemically, living proto- 

 plasm is an extremely unstable albuminoid substance, insoluble in water. 

 It is neutral or weakly alkaline in reaction. It undergoes heat stiffening 

 or coagulation at about 130 F. (54.5 0.), and hence no organism can 

 live when its own temperature is raised beyond this point. 



M;iny. of course, can exist for a time in a much hotter atmosphere, 

 since they possess the means of regulating their own temperature. 



Besides the coagulation produced by heat, protoplasm is coagulated 

 and therefore killed by all the reagents which produce this change in 

 albumen (see Appendix). If protoplasm be subjected to chemical 

 analysis, the chief substances of which it is found to consist belong to 

 the class of bodies called Proteids or albumins. These are bodies made 

 up of the chemical elements 0. H. N.~0. and S., in certain slightly 

 varying proportions. They are essential to the formation of protoplasm, 

 for without one or more of them, protoplasm cannot exist. Indeed some 

 would put this still more shortly, and say that protoplasm is living pro- 

 teid. Associated with proteids as an essential, is a certain amount of 

 water; but there are other bodies, non-essential, frequently present, and 

 varying under different circumstances; such as glycogen, starch, cellulose, 

 chlorophyll, fats, and the like. 



The protoplasmic substance of cells may undergo more or less essen- 

 tial modifications: thus, in fat cells we may have oil, or fatty crystals, 

 occupying nearly the whole cell; in pigment cells we find granules of 

 pigment; in the various gland cells the elements of their secretions. 

 Moreover, the original protoplasmic contents of the cell may undergo a 

 gradual chemical change with advancing age; thus the protoplasmic 

 cell-substance of the deeper layers of the epidermis becomes gradually 

 converted into keratin as the cell approaches the surface. So, too, the 

 original protoplasm of the embryonic blood-cells is infiltrated with the 

 haemoglobin of the mature colored blood-corpuscle. 



The vital or physiological characters of protoplasm are seen in the 

 performance of its functions. Many of these qualities are exceedingly 

 well illustrated in the microscopic animal called the Amoeba, which is a 

 monocellular organism found chiefly in fresh water, but also in the sea 

 and in damp earth. Under the same term no doubt more than one kind 

 of organism is included, but at any rate in each most of the vital 

 properties of protoplasm may well be studied. They are as follows: 



