October 14, 1915] 



NATURE 



89 



. onstituents of the cell which maintain persistently 

 md uninterruptedly their existence throughout the 

 whole life-cycle of living organisms universally. 



I hope t shall not be misunderstood when I enun- 

 ( late this apparently sweeping and breathless generali- 

 sation. I am perfectly aware that in the life-cycle of 

 my given species of organism there may be many 

 cell-constituents besides the chromatin-particles that 

 are propagated continuously through the whole life- 

 cycle ; but cell-elements which appear as constant 

 parts of the organisation of the cell throughout the life- 

 cycle in one type of organism may be wanting alto- 

 i^-^ether in other types. With the exception of the 

 hromatin-particles there is no cell-constituent that can 

 )<> claimed to pyersist throughout the life-cycles of or- 

 ganisms universally. It may be that this is only the 

 ■'■suit of our incomplete knowledge at the present 

 line. I am prepared, however, to challenge anyone 

 to name or to discover any cell-constituent, other than 

 the chromatinic particles, which are present through- 

 out the life-cycle, not merely of some particular 

 irganism, but of organisms universally. 



To recapitulate my argument in the briefest form; 

 the chromatinic constituents of the cell contrast with 

 all the other constituents in at least three points : 

 physiological predominance, especially in constructive 

 metabolism ; specific individualisation ; and perma- 

 nence in the sense of potential biological immortality. 

 Any of these three points, taken by itself, is sufficient 

 to confer a peculiar distinction, to say the least, on 

 the chromatin-bcJies; but taken in combination they 

 appear to me to furnish overwhelming evidence for 

 regarding the chromatin-elements as the primary and 

 essential constituents of living organisms, and as 

 representing that part of a living body of any kind 

 which can be followed by the imagination, in the 

 reverse direction of the propagative series, back to the 

 very starting-point of the evolution of living beings. 



In the attempt to form an idea as to what the 

 earliest type of living being was like, in the first place, 

 and as to how the earliest steps in its evolution and 

 differentiation came about, in the second place, we 

 have _ to ^ exercise the constructive faculty of the 

 imagination guided by such few data as we possess. 

 It is not to be expected, therefore, that agreement 

 can be hoped for in such speculations ; it would indeed 

 be very undesirable, in the interests of science, that 

 there should be no conflict of opinion in theories 

 which, by their very nature, are beyond any possi- 

 bility of direct verification at the present time. The 

 views put forward by any man do but represent the 

 visions conjured up by his imagination, based upon 

 the slender foundation of his personal knowledge, 

 more or less limited, or intuition, more or less falla- 

 cious, of an infinite world of natural phenomena. 

 Consequently such views may be expected to diverge 

 as widely as do temperaments. If, therefore, I venture 

 upon such speculations, I do so with a sense of per- 

 sonal responsibility and as one wishing to stiftiulate 

 discussion rather than to lay down dogma. 



To me, therefore, the train of argument that I have 

 set forth with regard to the nature of the chromatinic 

 constituents of living organisms appears to lead to the 

 conclusion that the earliest living beings were minute, 

 possibly ultramicroscopic particles which were of the 

 nature of chromatin. How far the application of the 

 term chromatin to the hypothetical primordial form of 

 life is justified from the point of view of substance, 

 that is to say in a biochemical sense, must be left 

 uncertain. In using the term chromatin I must be 

 understood to do so in a strictly biological sense, 

 meaning thereby that these earliest living things were 

 biological units or individuals which were the ances- 

 tors, in a continuous propagative series, of the 

 chromatinic grains and particles known to us at the 

 NO. 2398, VOL. 96] 



present day as universally-occurring constituents of 

 living organisms. Such a conception postulates no 

 fixity of chemical nature ; on the contrary, it implies 

 that as substance the primitive chromatin was highly 

 inconstant, infinitely variable, and capab'e of sf)ecific 

 differentiation in many divergent directions. 



For these hypothetical primitive organisms we 

 nttay use Mereschkowsky's term biococci. They must 

 have been free-living organisms capable of building 

 up their living bodies by synthesis of simple chemical 

 compounds. We have as yet no evidence of the exist- 

 ence of biococci at the present time as free-living or- 

 ganisms ; the nearest approach to any such type of 

 living being seems to be furnished by the organisms 

 known collectively as Chlamydozoa, which up to the 

 present have been found to occur only as pathogenic 

 parasites. In view, however, of the minuteness and 

 invisibility of these organisms, it is clear that they 

 could attract attention only by the effects they produce 

 in their environments. Consequently the human mind 

 is most likely to become aware in the first instance 

 of those forms which are the cause of disturbance in 

 the human body. If free-living forms of biococci exist, 

 as is very possible and even probable, it is evident that 

 very delicate and accurate methods of investigation 

 would be required to detect their presence. 



If it be permissible to draw conclusions with regard 

 to the nature of the hypothetical biococci from the 

 somewhat dubious, but concrete, data furnished by 

 the Chlamydozoa, the following tentative statements 

 may be postulated concerning them. They were (or are) 

 minute organisms, each a speck or globule of a sub- 

 stance similar in its reactions to chromatin. Their 

 substance could be described as homogeneous with 

 greater approach to accuracy than in the case of any 

 other living organism, but it is clear that no living 

 body that is carrying on constructive and destructive 

 metabolism could remain for a moment perfectly homo- 

 geneous or constant in chemical composition. Their 

 bodies were not limited by a rigid envelope or capsule. 

 Reproduction was effected by binary fission, the body 

 dividing into two with a dumbbell-shaped figure. 

 Their mode of life was vegetative — that is to say, 

 they reacted upon their environmental medium by 

 means of ferments secreted by their own body- 

 substance. The earliest forms must have possessed 

 the power 6f building up their protein-molecules from 

 the simplest inorganic compounds ; but different types 

 of biococci, characterised each by specific reactions and 

 Idiosyncrasies, must have become differentiated very 

 rapidly in the process of evolution and adaptation to 

 divergent conditions of life. 



Consideration of the existing types and forms of 

 living organisms shows that from the primitive bio- 

 coccal type the evolution of living things must have 

 diverged in at least two principal directions. Two 

 new types of organisms arose, one of which continued 

 to specialise further in the vegetative mode of life, 

 in all its innumerable variations, characteristic of the 

 biococci, while the other type developed an entirely 

 new habit of life — namely, a predatory existence. I 

 will consider these two types separately. 



(i) In the vegetative type the first step was that 

 the body became surrounded by a rigid envelope. 

 Thus came into existence the bacterial type of 

 organism, the simplest form of which would be a 

 Micrococcus, a minute globule of chromatin sur- 

 rounded by a firm envelope. From this familiar type 

 an infinity of forms arise by processes of divergent 

 evolution and adaptation. I will not attempt, how- 

 ever, to follow up the evolution of the bacterial type 

 further, or to discuss what other types of living 

 organisms may be affiliated with it, as I have no 

 claims to an expert knowledge of these organisms. 



(2) In the evolution from the biococcus of the pre- 



