68 



GENERAL PHYSIOLOGY 



characterises all other cells. There are also among animals varieties 

 of cells that show quite the same quantitative relation of the two 

 substances to each other ; an example of such is afforded by the 

 sperm-cells, or spermatozoa, which consist of a large quantity oi 

 nuclear substance and a very small quantity of protoplasm. 



Thus, from the present state of our knowledge, it appears that 

 among the organisms now living upon the earth there are no cells 

 in which a separation of two different substances is not present, 

 but that every cell possesses a nucleus in addition to the proto- 

 plasm. It is, of course, another question whether during the 

 evolution of living substance upon the earth organisms may not 

 have existed at some earlier time, in which the whole body 

 consisted of a single homogeneous substance, and no separation into 

 different substances had yet taken place. If such organisms ever 



PiQ. 9,— structure of various Bacteria. (After BUtsehli.) a, Bacterium lineola, normal and under- 

 going division. 6, Spirillum undula, c, Bactm-ium from stagnant water. 



existed, they could be ranked in comparison with real cells as cytodes, 

 as Haeckel terms non-nucleated elementary organisms. Notwith- 

 standing them, it must be granted that there belongs to the 

 conception of the cell at present, not only a single homogeneous 

 mass, the protoplasm, but also a substance differing from it, the 

 nuclear substance. Accordingly, Max Schultze's morphological 

 definition would be widened as follows : The cell is a hit of 

 protoplasm containing a distinct nucleus. 



If the protoplasm be examined with strong magnifying powers, 

 in many cells other distinct constituents besides the nucleus are 

 found embedded in the protoplasmic ground-substance. In many 

 cells oil-droplets occur, in others pigment-granules, in plant-cells 

 starch-grains, etc. ; but all these bodies do not occur in every kind 

 of cell : they are special, not general, cell-constituents. It appeared 



