THE CELLULAR CHANGES OF AGE 41 



therefore ever be honoured by all investigators of vital 

 phenomena. What the atom has been to the chem- 

 ist, the cell is to the naturalist, but with this differ- 

 ence, atoms are hypothetical, cells are known by 

 direct observation. Every cell consists of two essen- 

 tial parts. There is an inner central kernel which is 

 known by the technical name of nucleus, and a cov- 

 ering mass of living material which is termed the 

 protoplasm and constitutes the body of the cell. I 

 will now call for the first of our lantern slides to be 

 thrown upon the screen. It presents to you pictures 

 of the cells as they are found lining the mouth of the 

 European salamander. The two figures at the top 

 illustrate very clearly the elements of the cell. The 

 protoplasm forms a mass, exhibiting in this view no 

 very distinctive characteristics, and therefore offering 

 a somewhat marked contrast with the darker oval 

 nucleus, which presents in its interior a number 

 of granules and threads. Every nucleus consists 

 of a membrane by which it is separated from the 

 protoplasm, and three internal constituents : First, a 

 network of living material, more or less intermingled 

 with which is a second special substance, chromatine, 

 which owes its name to the very marked affinity 

 which it displays for the various artificial colouring 

 matters which are employed in microscopical re- 

 search. 1 The third of the internal nuclear constitu- 



1 It seems to me very doubtful whether the distinction drawn between the 

 network and the chromatine of the nucleus is valid but the distinction is 

 usually affirmed in the text-books of to-day. There are observations which 



