6o2 THE POPULAR SCIENCE MONTHLY. 



tion, Lave been changed into the new species. Prof. Cohn does not 

 doubt but that Darwin and his school may have over-estimated the 

 reach of the explanations given by him to account for the transmuta- 

 tion of species, and especially the importance of natural and sexual 

 selection, but the fundamental fact has been established, and will re- 

 main so for all future time. This fact is, that the collective life of the 

 earth, from the beginning even until now, and from the fungus-cell up 

 to man, represents a single series which has never once been broken, 

 whose members through direct propagation have proceeded out of each 

 other, and in the course of a vast period have been developed into 

 manifold and, on the whole, perfect forms. 



The sciences which are concerned with life have during late years 

 been cultivated on all sides ; even in earlier years Cuvier and Jussieu 

 had done as much for zoology and botany as the state of discovery in 

 their time permitted, but since 1858 the boundaries of both kingdoms 

 have been widely extended by the labors of Carpenter, Huxley, and 

 Pourtales. 



After referring to the researches of Goethe in the last century, and 

 those of Bauer and of Johannes Mtiller in the present, in reference to 

 the physiology of plants and animals, Prof. Cohn says it was only in 

 our own time, and first in 1843 in Schleiden's " Grundzugen der Wis- 

 senschaftlichen Botanik," that the new principle was followed out ; the 

 principle, namely, that all vegetable phenomena and all the various 

 forms of plants proceed from the life and the development of their 

 cells. After Schwann discovered that animal bodies also were built 

 up from an analogous cell, mainly by Virchow was then developed 

 from this principle the modern cellular physiology and pathology which 

 trace the condition both of healthy and diseased men and animals 

 back to the life-function of their cells. But, as the lecturer says, to 

 attempt to follow out the advances made by science in these directions 

 during the last twenty-five years would require a large volume, and 

 cannot be done in the space of a lecture or an article. 



Even the cell itself has been changed. Until Schleiden's time it 

 was a little bleb filled with fluid ; we now regard it as a soft glutinous 

 body constructed out of the albuminous protoplasm first distinguished 

 by Mohl in 1845, and which is covered with a cellular integument, as 

 the oyster is with its cell. After waxing eloquent over the cell as an 

 entity, an "ego" by itself, and its relations to the outer world, Prof. 

 Cohn says that science now teaches us that there is only one life and 

 one cell, the cell of plants and of animals being essentially the same. 

 The most highly-developed animal differs from the simplest plant only 

 in the number and greater development of the matter composing the 

 cells, but, above all, to the more complete elaboration {Arbeitstheilung), 

 and the stricter subordination of the separate cells to the collective 

 life of the organism. Between the two extremes of the living world, 

 the yeast-fungus and man, there is the same difference as there is be- 



