THE president's ADDRESS. 345 



living body, or substances which have come into existence by 

 the breaking down of the living matter, and which will be 

 eliminated eventually from it ; they may be compared generally 

 either to the fuel or the ashes of a fire. Such granules may 

 be classed generally as metaplastic bodies that is to say, as bodies 

 which are not, strictly speaking, a part of the living protoplasm 

 itself. 



In addition, however, to granules of temporary metaplastic 

 nature, there are certain other granules which appear to be of 

 the greatest importance in the economy of the living substance, 

 since they are of constant and universal occurrence in living 

 organisms of all kinds namely, the peculiar grains known as 

 ckromatin, so called on account of their property of taking up 

 certain colouring matters, a peculiarity by which they are 

 generally recognised. In organisms of the most simple type the 

 chromatin-grains are distributed usually throughout the whole 

 protoplasmic body, or the greater part of it ; but in the majority 

 of cases they are gathered together at one point, or more than 

 one, to form a structure termed the nucleus ^t\i?it is to say, the 

 kernel, as it were, of a certain mass or lump of the living 

 substance, which is then commonly termed a cell. The nucleus 

 varies greatly in structure in different cases, but consists always 

 of a collection of chromatin-grains combined with various 

 accessory substances and structures which may be termed collec- 

 tively achromatin. The chromatin-grains are the essential 

 element of the nucleus, which never contains any metaplastic 

 bodies of any sort. 



When a true nucleus is present, the protoplasm outside it, 

 constituting the cell-body, is commonly termed the cytoplasm ; it 

 may contain extranuclear grains of chromatin, so-called chro- 

 midia, or may be quite free from them. There is no essential 

 difference, however, between the cytoplasm of a nucleated 

 organism and the body- substance in those organisms in which the 

 chromatin-grains are scattered through the protoplasmic body 

 without being concentrated and organised into a nucleus ; we 

 may therefore use the word " cytoplasm " to designate the proto- 

 plasmic ground-substance or matrix apart from the chromatin- 

 grains, irrespective of whether a definite nucleus exists or not. 

 It is necessary to be clear about the meaning of the terms 

 used, in order to avoid confusion of thought, and in the present 



