THE 



MONTHLY MICROSCOPICAL JOURNAL. 



AUGUST 1, 1873. 



I. — Researches on the Life History of a Cercomonad : a 



Lesson in Bioge^iesis. 



By W. H. Dallinger, F.K.M.S., and J. Drysdale, M.D. 



Plates XXIV., XXV., and XXVI. 

 The question as to -whether vital forms of the lowliest and minutest 

 kind may have their origin in a new, and as yet unexplained, 

 arrangement of invital material, is one that can never find a 

 legitimate and final reply in the class of experiments employed 

 to test it within the last thirty years. A careful student of the 

 literature of the subject will see that the results obtained by the 

 same and different experimenters, with similar infusions and solu- 

 tions, are so uncertain, and often contradictory, as to leave the 

 whole question open to bias ; and an almost equal array of so- 

 called "experimental facts," from nearly equally trustworthy ob- 

 servers, may be quoted on either side. This may be all pleasant 

 enough in a " wordy war," but it does not even approximate to a 

 decision of the issue, and points to insufficiency in the experiments 

 employed. The appearance or non-appearance of organic forms in 

 certain infusions placed in sealed flasks or tubes, or otherwise con- 

 ditioned, is held to be decisive of their production de novo, or other- 

 wise ; but in point of fact, we know nothing — absolutely nothing — 

 of the life history of the greater number of the forms produced. To 

 attempt to decide, therefore, from the experiments as yet published, 

 that their production in gross masses in inorganic infusions proves 

 that inorganic elements produced them, may be to beg the whole 

 question. Inferring from what we hnow of nature's modes of re- 

 production, we have a right to expect not a de novo production, but 

 a production from genetic elements. But when we remember the 

 relation in size, throughout nature, between the ova and sperma- 

 tozoa and the organism producing them, the fact that no such 

 elements are visible (if they exist) in Bacteria or monads is probably 

 a mere necessity of our present instrumental power. At least this 

 is inevitable, that before we can be scientifically certain that these 

 lowly forms do or do not originate in non- vital elements, we ought 

 to know their life history ; and if this be desirable in the question 

 of Abiogenesis, it must be absolutely essential before we even 

 approach that of Heterogenesis. We must patiently follow them 

 VOL. x. r 



