The Cellular Basis 129 



entiations in the course of development and it constitutes in the 

 main the body plasm or somatoplasm. Germplasm and somato- 

 plasm are not, therefore, vague generalizations, but they are defin- 

 ite cell substances which may be seen under the microscope. 



5. The Units of Living Matter. The entire cell, nucleus and 

 cytoplasm, is the smallest unit of living matter which is capable 

 of independent existence. Neither the nucleus nor the cytoplasm 

 can for long live independently of each other, but the entire cell 

 can perform all the fundamental vital processes. It transforms 

 food into its own living material, it grows and divides, it is capa- 

 ble of responding to many kinds of stimuli. But while the parts of 

 a cell are not capable of independent existence they may be dif- 

 ferentiated to perform different functions. 



Panmerism. Not only is the cell as a whole capable of assimi- 

 lation, growth and division, but every visible part of the cell has 

 this power. The nucleus builds foreign substances into its own 

 substance, and after it has grown to a. certain size it divides into 

 two; the cytoplasm does the same, and this process of assimila- 

 tion, growth and division occurs in manv parts of the nucleus 

 and cytoplasm, such as the chromosomes, chromomeres, centro- 

 sorries, etc. In all cases cells come from cells, nuclei from nuclei, 

 chromosomes from chromosomes, centrosomes from centro- 

 somes, etc. 



Indeed, the manner in which all living matter grows indicates 

 that every minute particle of protoplasm has this power of taking 

 in food substance and of dividing into two particles when it has 

 grown to maximum size ; this is known as panmerism. Presum- 

 ably this power of assimilation, growth and division is possessed 

 by particles of protoplasm which are invisible with the highest 

 powers of our microscopes, though it is probable that these par- 

 ticles are much larger than the largest molecules known to chem- 

 istry. The smallest particle which can be seen with the most 

 powerful microscope in ordinary light is about 250 ftp, (millionths 

 of a millimeter) in diameter. The largest molecules are prob- 



