ORGANIC CHEMISTRY AND CELL DIVISION 



97 



won more than a million dollars for the twenty-eighth nail alone, it is 

 easy to understand what a division of cells may bring about in a short 

 time ; especially when it is remembered that the tiny bacteria, which 

 are single-celled plants, may multiply and divide in such way every few 

 minutes. In the course of one or two hours, where division is suf- 

 ficiently rapid, there are millions upon millions of cells where there was 

 only one before. 



Textbooks say there are two ways in which cell division conies 

 about, but recent investigations tend to show that this is in error and 

 that all cell division is mitotic. One method was said to be the shorter 



Fig. 29. Diagrams Representing the Essential Phenomena of Mitosis. 

 A, a cell with resting nucleus containing a chromatic reticulum and a single 

 nucleolus. The centrosome is double and surrounded by the centrosphere. B, the 

 centrosomes are separating and each is surrounded by astral rays ; the chromatin 

 forms a convoluted thread or spireme. C, the spireme is broken up into a number 

 of V-shaped chromosomes, the polar spindle is formed between the now widely 

 separated centrosomes. D, the chromosomes attached to the spindle-fibres are 

 arranged at the equator of the spindle. E, division of the chromosomes, which are 

 viewed end on. F, divergence of the chromosomes. G, chromosomes collecting at the 

 poles of the spindle, the space between them occupied by interzonal fibres ; commence- 

 ment of division of cell-body. H, I, complete division of the cell, and reconstitution of 

 the nuclei. In / the centrosomes are dividing preparatory to a new mitosis. Note 

 A-Z>=prophase ; =:metaphase ; F, G=anaphase; H, 7=telophase. (After Bourne.) 



and simpler way, in which the cell, without any previous changes that 

 could be observed, split in two parts. But the longer method, known 

 as mitosis (Fig. 29), is the more common, and is the one whicti must 

 be studied in detail if any understanding whatever is to be obtained as 

 to how plants and animals evolve from the single original cell to the 

 marvelous complex organisms into which they develop in adult life. 



The cell, as has just been described in the last chapter, has a net- 

 work in the nucleus that stains quite easily and readily. In the normal 

 condition such a cell is said to be in the resting stage. In the higher 

 forms cell division takes place only after fertilization, that is, after the 

 male sperm has united with the female egg. The chromatin, or stained 

 nuclear network, begins a process by which the stained part separates 

 from all of the other network, taking upon itself the shape of a single 

 thread or skein. A little later, this skein of chromatin breaks up into small 



