ANIMAL AND VEGETABLE 105 



often found divided in the apparently resting nucleus, the 



two particles being united by a small system of fibres forming 



a minute spindle at one side of 



the nucleus. When mitosis is 



about to take place this spindle 



enlarges, and as the changes in 



the chromatin of the nucleus \ 



occur which changes involve 



the disappearance of the nuclear rf ~15~~ 



membrane the spindle gradually 



passes into the middle of the mitotic nucleus, and with 



the fibres of the spindle therefore completely traversing 



the nucleus. (Fig. 15.) 



" The spindle-fibres appear to form directing lines, along 

 which the chromosomes pass, after the cleavage, towards the 

 nuclear poles to form the daughter nuclei." * 



In most animal cells the protoplasm becomes constricted 

 into two parts midway between the two daughter nuclei* 

 " Each daughter cell so formed retains one of the two 

 attraction-particles of the spindle as its centrosome, and 

 when the daughter cells are in their turn again about to 

 divide, this centrosome divides first and forms a new spindle, 

 and the whole process goes on as before." (Schafer.) 



To go back a little, to the properties of living matter, 

 we learn that " living cells exhibit irritability or the pro- 

 perty of responding to stimuli," electrical or otherwise, 

 much in the same way that nerve and muscle exhibit it 

 and I think we can postulate it as almost, if not quite, 

 unanswerable that to respond to electrical stimulus the 

 structure itself must be to some extent electrical. That 

 it exhibits irritability under mechanical, chemical, or 

 thermal stimuli does not affect the question, because a 

 stimulus of any kind must disturb the equilibrium of an 

 electrical unit of so delicate and sensitive a nature. 

 * The italics are my own. 



