PRESIDENTIAL ADDRESS. 455 



'however, of the miiiiuteness and invisibility of these organisms, it is clear that 

 tthey could attract attention only by the effects they produce in their environ- 

 •nient. Consequently the human mind is most likely to become aware in the 

 Ifirst 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. 



I am well aware that the nature and even the existence of the so-called 

 iChlamydozoa is uncertain at the present time, and I desire to exercise great 

 •caution in basing any arguments upon them. In the descriptions given of them, 

 liowever, there are some points which, if correctly stated, seem to me of great 

 importance. They are alleged to appear as minute dots, on the borderline of 

 "microscopic visibility or beyond it; they are capable of growth, so that a given 

 ■species may be larger or smaller at different times; their bodies stain with the 

 •ordinary chromatin-stains ; and they are stated to reproduce themselves by a 

 ■process of binary fission in which the body becomes dumbbell-shaped, appearing 

 as two dots connected by a slender thread, -which is drawn out until it snaps 

 :across and then the broken halves of the thread are retracted into the daughter- 

 bodies. This mode of division, strongly reminiscent of that seen in centrioles, 

 ^appears to me to permit of certain important conclusions with regard to the 

 ■nature of these bodies; namely, that the minute dot of substance has no firm 

 limiting membrane on the surface and that it is of a viscid or semi-fluid 

 consistence. 



If it be permissible to draw conclusions with regard to the nature of the 

 hypothetical biococci from the somewhat dubioue, but concrete data furnished 

 by the Chlamydozoa, the following tentative .statements may be postulated con- 

 cerning them. They were (or are) minute organisms, each a speck or globule 

 of a substance 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 

 homogeneous or constant in chemical composition. Their bodies were not 

 limited by a rigid envelope or capsule. Reproduction was effected by l)inary 

 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 

 mediiun by means of ferments secreted by their own body-substance. The 

 earliest forms must have possessed the power of building up their proteins- 

 molecules from the simplest inorganic compounds ; but different types of 

 biococci, characterised each by specific reactions and idiosyncrasies, muet 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 biococcal 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. 



(1) In the vegetative type the first step was that the body became sur- 

 rounded 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 surrounded by a firm envelope. From this familiar type an 

 infinity of forms arise by processes of divergent evolution and adaptation. 

 With increase in size of the body the number of chromatin-grains within the 

 envelope increase in number, and are then seen to be imbedded in a ground- 

 substance which is similar to cytopla.sm, apparently, and may contain non- 

 ehromatinic enclosures. With still further increase of size the chromatin-grains 

 also increase in number and may take on various types of arrangement in 

 clumps, spherical masses, rodlets. filaments straight or twisted in various ways, 

 or even irregular strands and networks," and the cytoplasmic matrix, if it is 



-- See especially Dobell, ' Contributions to the Cvtologv of the Bacteria,' 

 Qiinrt. Jourv. Mir.r. Srienrr. Ivi. (1911), pp. 461, 462. I cannot follow Dobell 

 in applying the term ' nuclei ' to these various arrangements of the chromatin,- 



