CHAPTER VI. 

 THE VITAL PHENOMENA OF THE CELL. 



I. Reproduction of the Cell by Division. One attri- 

 bute of the cell, which is of the greatest importance, since the 

 maintenance of life depends upon it, is its power of producing new 

 forms similar to itself, and by this means maintaining its species. 

 It is becoming daily more and more clearly evident, as the result 

 of innumerable observations, that new elementary organisms can 

 only arise through the division of the mother-cell into two or more 

 daughter-cells (Oram's cellula e cpIIuIo). This fundamental law, 

 which is of paramount importance in the study of biology, has 

 only been established after much laborious work along the most 

 diverse lines, and after many blunders. 



1. History of Cell Formation. Schleiden and Schwann (I. 

 28, 31), in developing their theories, asked themselves the natural 

 question, "How do cells originate?' Their answer, based upon 

 observations both faulty and insufficient, was incorrect. They 

 held that the cells, which they were fond of comparing to crystals, 

 formed themselves, like crystals, in a mother-liquor. Schleiden 

 named the fluid inside the plant cell Cytobl 'astern. He considered 

 it to be a germinal substance, a kind of mother-liquor. In this 

 the young cells were supposed to originate a solid granule, the 

 nucleolus of the nucleus developing first, around which a layer of 

 substance was precipitated ; this, they considered, became trans- 

 formed into the nuclear membrane, whilst fluid penetrated between 

 it and the granule. The nucleus thus formed constituted the cen- 

 tral point in the formation of the cell, in consequence of which it 

 was termed the Gijtoblast. The process of cell development was then 

 supposed to be similar to the one described above when the nucleus 

 was formed round the nucleolus. The cytoblast surrounded itself 

 with a membrane which was composed of substances precipitated 

 from the cell-sap. This membrane was at first closely in contact 

 with the nucleus, but later on was pushed away by the in-pressing 

 fluid. 



177 H 



