MODERN BIOLOGY 537 



expressed. And they are as much of a chemical as of a physical nature; the 

 physical phenomena — movement of various kinds — are invariably in- 

 duced and brought about by chemical reactions and in their turn produce 

 new reactions. 



Plasma ttoeories 

 BiJTscHLi's froth theory is an essentially physical attempt to explain the 

 structure of protoplasm. He certainly repeatedly points out the chemical 

 reactionary phenomena of the cell, but he pays little attention to them. 

 Taking as his basis the strongly vacuolized substance of the lowest pro- 

 tozoa, especially of the amoeba;, with the current-phenomena visible therein, 

 he conceives the living protoplasm as a fluid mass identical in its structure 

 with the emulsion that is obtained when oil and soda-solution are shaken 

 together. This purely mechanical emulsion-theory he afterwards elaborated 

 after making a series of experiments of a very ingenious character. Through 

 the mixture of variously composed liquids both he and a whole school of 

 investigators after him succeeded in imitating in a surprisingly natural way 

 a great many of the most complicated movements and structures of the liv- 

 ing cell-substance. It cannot, of course, be denied that the mechanical phe- 

 nomena which were found in these experiments to cause the movements in 

 the given substratum may also be capable of asserting their influence upon 

 the plasma movements, but as a reproduction of the phenomena of life these 

 experiments possess the fundamental fault of entirely disregarding the chem- 

 ical reaction that is incessantly going on in living substance; the mobile 

 oil-emulsion remains chemically what it was, whereas a creeping amoeba 

 is continually changing its chemical composition, so that movement and 

 chemical reaction are indissolubly dependent upon each other. In connex- 

 ion herewith we find also the belief, which has proved unsatisfactory from 

 the very beginning, that the fundamental substance of life is fluid — a the- 

 ory that has been considerably revised by modern colloid chemistry, of which 

 we shall have more to say presently. 



Flemming's plasma theory undeniably takes more account of chemical 

 conditions. According to this theory, protoplasm consists of a network of 

 fibres embedded in a homogeneous substance. These structures he found par- 

 ticularly in the cellular mass in various tissue-elements: in egg-cells and in 

 cartilaginous and glandular cells in higher animals. He believes the phenom- 

 ena of metabolism in the cell to be accompanied by changes in the filament 

 mass and in the basic substance, which should be examined in detail in 

 different subjects. The threads may sometimes be dissolved into canals and 

 vacuoles and thereby convey the assimilation products not only to different 

 places within the cell, but also between various cells, for these latter are 

 in most cases demonstrably connected with one another by bridges of fila- 

 ments. Thus the cells become the structural elements in the body, though 



