THE NEW CELL DOCTRINE 



17 



for the explanation of life until we shall know how the 

 chemical alterations go on in the living substance, which 

 is a highly complicated mixture of many organic combina- 

 tions of various sorts, all earned by great quantities of 

 water. 



A good example 

 of the complica- 

 tion of the phe- 

 nomena is offered 

 us by the condition 

 of the nucleus in 

 certain unicellular 

 organisms. In the 

 cells of the highest 

 plants and ani- 

 mals the nucleus is 

 always a simple 

 unit, but there are 

 many species of 

 protozoa known in 

 which the nucleus 

 is double, so that 

 there appear to be 

 two nuclei of un- 

 equal size Fig. 12. Fio. 12. — A unicellular animal, an infusorium (Nassau 

 I", |_ 1 ,. elegans). Natural length o.i mm. 9, Macronucleus; 



It nas been dlS- ^^^ micronucleus.— ^//er Schewiahof, from Lang's 

 covered that the VergUichende Anatomie. 



larger nucleus 



plays a role in the nutrition and growth of the cell while 

 the smaller nucleus has assumed exclusively the functions 

 which lead to the division of the cell. Nature makes here 

 for us an experiment in that she has separated in space the 



