70 THE POPULAR SCIENCE MONTHLY. 



every ^^^ is originally a simple cell. The seminal elements of the 

 male are also only simple cells, and the entire mysterious process of 

 fructification is after all nothing but the fusion or concrescence of two 

 different cells, the one a female egg-cell, and the other a male semen- 

 cell. In consequence of this fusion the germs of the two combined 

 cells dissolve, and therewith tltlj young, newly-generated individual 

 begins his existence as a simple cytod, or a small germless ball of 

 protoplasm. But inside of this cytod soon arises a new germ, which 

 turns it again into a cell, and this simple cell forms by oft-repeat-ed 

 segmentation an accumulation of cells. Out of this heap are produced 

 by secretion certain germinal layers or "germ-leaves," and out of 

 these proceed all the other organs of the complete being. Each of these 

 organs again originally consists only of cells, and in all of these cells 

 the essential constituent parts are only the germ and protoplasm: the 

 germ as the elementary organ of j^ropagation and heredity, protoplasm 

 as the elementary organ of all the other functions, sensation, motion, 

 alimentation, and adaptation. Cells and cytods, therefore, are true ele- 

 mentary organisms, independent minute forms of life, which either in 

 the lowest existences continue to live independently, or in the higher 

 organisms combine in numbers to form a community. Cells and cytods 

 are the veritable "formers" of life, or plastids. The most ancient 

 and primordial forms of plastids are cytods, the whole body of which 

 consists of protoplasm, in which the germs are internally produced, and 

 from which therefore the cells proceed. 



As a matter of course, to the infinite varieties presented by the 

 organic forms and vital phenomena in the vegetable and animal king- 

 dom, corresponds an equally infinite variety of chemical composition 

 in the protoplasm. The most minute homogeneous constituents of this 

 " life-substance," the protoplasm molecules, or plastidules, as they are 

 called by Elsberg, must in their chemical composition present an infi- 

 nite number of extremely delicate gradations and variations. The 

 atoms of carbon, hydrogen, nitrogen, oxygen, and sulphur, which 

 compose each of the plastidules, must enter into an infinite number of 

 diverse stratifications and combinations. The chemistry of to-day, 

 with its imperfect methods of investigation, is totally powerless before 

 these intricate organic compounds, and it is possible only to surmise, 

 from the infinitely varied physiological qualities of the numberless 

 kinds of plastids, the infinite variety of plastidules out of which they 

 are composed. 



According to the plastid theory recently advanced, the great 

 variety of vital phenomena is the consequence of the infinitely deli- 

 cate chemical difference in the composition of protoplasm, and it con- 

 siders protoplasm to be the sole active life-substance. This theory 

 puts force and matter in living organisms into the same causal con- 

 nection which has long been accepted for force and matter in inor- 

 ganic bodies. This conception has been rapidly matured, especially in 



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