GREAT STEPS IN ORGANIC EVOLUTION 855 



them, what position are we to assign to that yet farther depth of 

 underworld life, of which the existence has been demonstrated by 

 the pathologist as the specific organic infections of various diseases, 

 whose extreme minuteness is such as to pass through those finest of 

 filters which arrest the minutest bacteria and their spores; and 

 which thus long remained unseen with the highest microscopic 

 powers ? Yet in the case of the cancer infective organism, the brilliant 

 investigation of Gye and Barnard, with the former's skill in culture 

 and the latter's rare originality of microscopic device, has detected 

 this ; though still without attaining to adequate definition of form or 

 structure, to which neither microscope nor ultra-microscope attains. 



Yet here, and with other such filter-passers, the infective powers 

 prove living activity; so we have to deal with a form of living 

 matter which we cannot yet positively identify as belonging to the 

 bacterial level of being. It may indeed prove necessary to assign to 

 this a distinct character and position of its own, despite analogous 

 variety and adaptivity of life-ways, as the various diseases caused 

 by such infections show — witness smallpox, hydrophobia, foot-and- 

 mouth disease, cancer, etc. Are we perhaps thus reaching down into 

 a more or less completely precellular world, structurally at least 

 below that of bacteria, as they below fully cellular organisms? 

 It, of course, remains to be settled whether after all, as commonly 

 supposed, these are not rather comparable to the minutest known 

 micrococci and bacterium spores, and only minuter, by the degree 

 which prevents their arrest by the filter; or perhaps divested of 

 their resistant coating, and thus viscously passing through its narrow 

 spaces. Yet when we take into account the measured dimensions of 

 the smallest visible spores, and the far smaller apertures of the filter, 

 do we not find an order of minuteness for these infection-bodies 

 which begins to approach towards the (now approximately com- 

 puted) magnitudes of protein molecules? If so, must not an aggrega- 

 tion of these be so small as to render even the simple bacterium-spore 

 structure hardlj^ if at all, possible ? 



Be this as it may turn out, as investigation advances, there can 

 now be no doubt that just as the ordinary microscopic research of 

 naturalists has long revealed the cellular world in all ordinary life, 

 though beyond ordinary vision, and just as the bacteriologist has 

 gone yet deeper, so here we seem in the presence of a lower and 

 minuter life-form stiU ; and one bringing us nearer that of molecular 

 structure and process, which the biochemist is not only analysing 

 out, but even building up synthetically, in his own skilful and 

 subtle ways. Among these minutest of life-forms, still so imperfectly 

 known, is there not opening for him a new clue, even a new field of 

 research, linking up the bacteriologist's and pathologist's with his 

 own, and so with possible new light on the nature of life-processes, 

 the building up of life-structures ? 



