304 SCIENCE PROGRESS 



The chromatin-substance receives its name from its peculiar 

 property of combining with certain dyes, whereby it can be 

 coloured selectively and differentiated more or less completely 

 from the rest of the protoplasm. The staining test is, however, 

 a very inadequate and untrustworthy method of recognising 

 the substance. Our conception of chromatin should rather be 

 founded upon its relations to the life of the organism as a 

 whole and to its vital activities ; these relations I can only indicate 

 very briefly and summarily, so far as they are known. To begin 

 with, the chromatin-substance is never absent from any known 

 organism, however minute or apparently simple in structure : 

 direct experiment has shown that a cell deprived of its nucleus 

 cannot maintain its life during any length of time and is unable 

 to initiate any of its characteristic vital activities. The repro- 

 duction of a cell or of a simple protoplasmic organism always 

 involves division into two or more parts and in this process 

 the chromatin-substance divides first and is partitioned amongst 

 the daughter-individuals. In many cells, the nucleus divides 

 by a very elaborate mechanism known as karyokinesis, which 

 ensures an exact quantitative and qualitative partition of the 

 chromatin between each of the two daughter-nuclei. Through- 

 out the series of living beings, wherever sexual phenomena are 

 observed, the sexual act consists essentially in the union of 

 chromatin from two distinct organisms ; the ascertained facts 

 of fertilisation and development have led to the belief which, 

 if not universal, is at least very widely spread among biologists, 

 that the chromatin-grains determine the characters of the off- 

 spring and are the carriers of hereditary tendencies and pro- 

 perties. In the internal economy of the cell, the special function 

 of the nucleus appears to be that of producing the peculiar 

 substances known as ferments or enzymes, substances which 

 perhaps more than any other are characteristic of living bodies. 



These data, taken together, in my humble opinion constitute 

 a very strong case for regarding the nuclear substance, chro- 

 matin, as the all-important and essential constituent of living 

 organisms. Such a conclusion is greatly strengthened by the 

 fact that some of the minutest forms of life appear to consist 

 entirely or almost entirely of chromatin. Apart from the 

 Chlamydozoa, the true nature of which can hardly be said to 

 be established with certainty at present, many instances could 

 be cited of organisms or stages of organisms in which the body 





