SPECULATIONS ON THE ORIGIN OF LIFE 303 



forced to believe that a condition in which a living body consisted 

 only of one form or type of living matter preceded that in which 

 the body was composed of two or more structural components. 



It is, I think I may say, the most generally accepted notion 

 among biologists that the cytoplasmic substance of the cell (to 

 which the term "protoplasm" is often restricted) is to be regarded 

 as the primitive living matter. The earliest forms of life have 

 been supposed to be formless masses of protoplasm, without 

 nuclei, the so-called Monera of Haeckel. From such a condition 

 true cells are supposed to have arisen by individualisation of 

 the indefinite mass and acquisition of a specific form and size, 

 together with the differentiation of a nucleus, which on this 

 view would represent the oldest cell-organ but not an essential 

 or indispensable part of a living body. For my part, I find 

 myself obliged to dissent entirely from any such view. 

 Although a definite nucleus, a body of complex structure and 

 organisation, such as we find in the tissue-cells of animals and 

 plants, is undoubtedly to be regarded as a relatively late product 

 of evolution, I believe, nevertheless, that the nucleus contains 

 the oldest and most primitive elements of the living substance 

 and that the earliest forms of life consisted entirely of the 

 characteristic and essential material of the nucleus. In order 

 to elaborate this view further, I must discuss as briefly as 

 possible the nature and constitution of the nucleus. 



In different cells the nucleus is seen to vary almost infinitely 

 in form, structure and composition ; but this diversity only 

 brings into greater relief the fact that common to all nuclei is 

 the presence amongst the contents of a peculiar substance 

 termed chromatin, 1 which occurs in the form of granules or 

 masses distributed in various ways over the framework of the 

 nucleus. In addition to the chromatin contained within the 

 nucleus, however, there may also be grains of chromatin 

 scattered through the cytoplasm, so-called chromidia. In many 

 organisms, finally, a true nucleus may be temporarily absent, 

 the chromatin-substance being present only in the diffused or 

 chromidial condition. 



1 In the course of the discussion Prof. M. Hartog challenged me to give a 

 definition of chromatin ; I replied that I would almost as soon attempt to define 

 life itself. I may add that I have discussed the question of the nature of chromatin 

 at greater length in my recently published work, An Introduction to the Study of 

 the Protozoa (Arnold, 191 2). 

 20 



