114 THE STORY OF THE LIVING MACHINE. 



while in the process of fertilization the centro- 

 some is handed down from parent to child, there 

 are some reasons for believing that it may dis- 

 appear in subsequent cells, and later be redevel- 

 oped out of other parts. The only part of the 

 cell in which complete continuity from parent to 

 child is demonstrated, is the nucleus and particu- 

 larly the chromosomes. All of these facts simply 

 emphasize the importance of the chromosomes, 

 and tell us that these bodies must be regarded as 

 containing the most important features of the cell 

 which constitute its individuality. 



What is Protoplasm ? Enough has now been 

 given of disclosures of the modern microscope 

 to show that our old friend Protoplasm has as- 

 sumed an entirely new guise, if indeed it has not 

 disappeared altogether. These simplest life pro- 

 cesses are so marvelous and involve the action of 

 such an intricate mass of machinery that we can 

 no longer retain our earlier notion of protoplasm 

 as the physical basis of life. There can be no 

 life without the properties of assimilation, growth, 

 and reproduction ; and, so far as we know, these 

 properties are found only in that combination of 

 bodies which we call the cell, with its mixture of 

 harmoniously acting parts. Life, at least the life of 

 a cell, is then not the property of a chemical compound 

 protoplasm, but is the result of the activities of a ma- 

 chine. Indeed, we are now at a loss to know how 

 we can retain the term protoplasm. As originally 

 used it meant the contents of the cell, and the sig- 

 nificance in the term was in the conception of pro- 

 toplasm as a somewhat homogeneous chemical 

 compound uniform in all types of life. But we now 

 see that this cell contains not a single substance, 

 but a large number, including solids, jelly masses, 



