BACTERIA AND THEIR ALLIES 161 



organisms are produced from a Rotifer's egg ; or when even 

 Ciliated Infusoria are produced from large encysted Amoebas or 

 from the great eggs of a Hydatina.' These examples will help to 

 bring home to the reader what is meant by Heterogenesis, 

 when I say it is a process in which we have the actual substance 

 of organisms or their germs giving rise to alien forms of life. 



The Heterogenetic Origin of Bacteria and their Allies. 



In such instances as I have just cited it is easy to see that actual 

 portions of the living matter of the transforming organism or germ 

 are converted, bulk for bulk, into new organisms of a totally 

 different kind. But in most of the cases in which Bacteila and 

 their allies, or Torulze, are produced in or from the substance of 

 other organisms, whether animal or vegetal, it is practically 

 impossible to say for certain that their origin has been by 

 Heterogenesis rather than by Archebiosis. Such organisms seem 

 always to present themselves iirst in cells or tissues as extremely 

 minute motionless particles^ — sometimes where no particles of any 

 kind were previously visible, and sometimes intermixed with 

 particles of a different order, but from which they cannot readily 

 be discriminated. And where the particles of living matter, so 

 individualising themselves, are so small as to be almost beyond the 

 range of our most powerful microscopes, it is impossible to say, 

 until they begin to assume specific shapes, or particular modes of 

 collocation, that they are not normal constituent granules of the 

 tissues in which they are found. But their invariable first 

 appearance as minute, motionless particles, rather than as active, 

 developed organisms, will be found to be a point of great 

 importance. 



Whenever Bacteria or their allies appear in the midst of the 

 tissues or fluids of animals or plants, two possibiUties have to be 

 thoroughly considered and excluded, before their presence can be 

 ascribed to Heterogenesis. The two possibilities that have to be 

 considered are these : — 



(o) Are the bodies of plants and animals interpenetrated in all 

 parts by visible or invisible germs of microorganisms, or are they 

 germless ? 



(6) Have the microorganisms which may be found in the tissues 

 or fluids of plants and animals under various conditions been 



' All such, and many other, processes are described, and illustrated by photo- 

 micrographs, in the writer's "Studies in Heterogenesis," 1904 ; and many of those 

 above mentioned are also described in the present worli. 



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