PROTOPLASM AND LIFE. 727 



their preservation to the presence of the hard, persistent structures 

 secreted by their protoplasm, and must, after all, have formed but a 

 very small proportion of the unicellular organisms which peopled the 

 ancient world, and there fulfilled the duties allotted to them in nature, 

 but whose soft, perishable bodies have left no trace behind. 



In our own days similar unicellular organisms are at work, taking 

 their part silently and unobtrusively in the great scheme of creation, 

 and mostly destined, like their predecessors, to leave behind them no 

 record of their existence. The Red-Snow plant, to which is mainly 

 due the beautiful phenomenon by which tracts of Arctic and Alpine 

 snow become tinged of a delicate crimson, is a microscopic organism 

 whose whole body consists of a simple spherical cell. In the proto- 

 plasm of this little cell must reside all the essential attributes of life ; 

 it must grow by the reception of nutriment ; it must repeat by mul- 

 tiplication that form which it has itself inherited from its parent ; it 

 must be able to respond to the stimulus of the physical conditions by 

 which it is surrounded. And there it is, with its structure almost on 

 the bounds of extremest simplification, taking its allotted part in the 

 economy of nature, combining into living matter the lifeless elements 

 which lie around it, redeeming from sterility the regions of never- 

 thawing ice, and peopling with its countless millions the wastes of the 

 snow-land.* 



But organization does not long rest on this low stage of unicellular 

 simplicity, for, as we pass from these lowest forms into higher, we find 

 cell added to cell, until many millions of such units become associated 

 in a single organism, where each cell, or each group of cells, has its 

 own special work, while all combine for the welfare and unity of the 

 whole. 



In the most complex animals, however, even in man himself, the 

 component cells, notwithstanding their frequent modification and the 

 usual intimacy of their union, are far from losing their individuality. 

 Examine under the microscope a drop of blood freshly taken from the 

 human subject, or from any of the higher animals. It is seen to be 

 composed of a multitude of red corpuscles, swimming in a nearly color- 

 less liquid, and along with these, but in much smaller numbers, some- 

 what larger colorless corpuscles. The red corpuscles are modified 

 cells, while the colorless corpuscles are cells still retaining their typical 

 form and properties. These last are little masses of protoplasm, each 

 enveloping a central nucleus. Watch them. They will be seen to 

 change their shape ; they will project and withdraw pseudopodia, and 

 creep about like an Amoeba. But, more than this, like an Amceba, 

 they will take in solid matter as nutriment. They may be fed with 



* The Red-Snow plant (Protococcus nivalis) acts on the atmosphere through the agen- 

 cy of chlorophyl, like the ordinary green plants. As in these, chlorophyl is developed 

 in it, and is only withdrawn from view by the predominant red pigment to which the 

 Protococcus owes one of its most striking characteristics. 



