MNNEAN iSOCiETl' C)l' LONDON. bl 



(2) Chi'oinatiu, occurring as minute granules iiubeddecl in the 

 cytoplasm, and either scattered in it, or aggregated wholly or i:i 

 part to form a definite nucleus. 



The question at once arises, which of these two constituents of 

 protoplasm represents the true li\ing matter? Is the cytoplasm, 

 or the chromatin, to be regarded as the primary living substance? 



No answer that may be attempted to this question can be 

 regarded as in any way final in the 'present state of our knowledge, 

 and the subject can hardly be discussed adequately in a brief 

 space : but the following are a few of the laost important facts 

 upon which to found a judgment : — 



I. No living organism is known with certainty which does not 

 contain substance of the nature of chromatin ; and some of the 

 minutest organisms, e.;/. some Bacteria and Spirochaetes, seem to 

 consist of chromatin alone. These facts indicate that cliromatin 

 is, and cytoplasm is not, a constant constituent of living bodies. 



II. By experiment it is found that cells, if deprived of the 

 nucleus and reduced to cytoplasm aloue, cannot continue living 

 for long, and cannot initiate vital changes or processes. 



Til. The present state of our knowledge tends to establish as a 

 general truth that the chromatin-elements are the governing and 

 directing bodies of cells, and as such are the bearers of hereditary 

 tendencies. 



From these data the conclusion seems to me irresistible, that 

 chromatin is the primary living substance, not cytoplasm. 



If then chromatin is a substance of such immense importance in 

 living things, it becomes necessary to attempt to define or charac- 

 terize it further — a very difficult task In the first place, it is found 

 that the chromatin-elements of the nucleus consist of, or contain, 

 substances of greater complexity from the chemical point of view, 

 than the other portions of the protoplasm. In the second place, 

 this complexity is combined with a high degree of variability, as 

 might indeed have been expected on general grounds. For since 

 the vital activities and pi'operties manifestly differ in every species 

 of organism, and even, it might be said, in every individual cell, 

 then, if the chromatin-substance be the regulating and deter- 

 mining cause of tlie vital activities and manifestations, it follows 

 that tlie chromatin must differ to a corresponding degree in each 

 case ; and therefore no given sample of chromatin can be expected 

 to be identically similar to any other sample. It is a matter of 

 common knowledge that such differences do occur between the 

 chromatin-elements of different organisms, and even in the same 

 organism at different periods of the life-cycle ; to take only the 

 micro-chemical test most commonly emi)loyed for the identifica- 

 tion of chromatin, namely its affinity for certain colouring-matters, 

 it can be said at once that there is no stain which can be relied 

 upon either to tinge the chromatin-elements of any organisms at 

 all times, or to stain only chromatin. 



LINN. SOC. rilOCEBDINGS. — SESSION 1909-1010. g 



