No. 590] THE EVOLUTION OF THE CELL 111 



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 environment. 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. 



I am well aware that the nature and even the existence 

 of the so-called Chlamydozoa 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, 

 however, there are some points which, if correctly stated, 

 seem to me of great importance. They are alleged to ap- 

 pear as minute dots, on the borderline of microscopic visi- 

 bility 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 daugh- 

 ter-bodies. This mode of division, strongly reminiscent 

 of that seen in centrioles, appears to me to permit of cer- 

 tain 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 

 dubious, but concrete data funished 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 reac- 

 tions to chromatin. Their substance could be described 



