298 CONCLUSION 



of Bacteria and their allies have been conducted under aseptic 

 conditions, and with all necessary precautions against the possibility 

 of infection. While in regard to many other observations that 

 have been made — touching the heterogenetic origin of Amoebae, 

 Monads, Peranemata and Ciliated Infusoria — it must be seen that 

 these, if made at all, have to be made on organisms either in their 

 own or in experimentally varied environments ; that, in either case, 

 aseptic conditions, or absolute isolation of the organisms under 

 observation, is always an impossibility ; and that any attempts in 

 this direction would inevitably stop the changes hitherto in progress. 

 In regard to the objection that there has not been a continuous 

 watching of the alleged heterogenetic changes, from start to finish, 

 on the same individual organism, I can only say that compliance 

 with such demands would not only be fruitless but would go far to 

 render for ever impossible any knowledge of heterogenesis. More- 

 over, the observation of different stages of change in different 

 individuals is, after all, the mode by which, as is well known, 

 multitudes of embryological investigations have to be conducted. 

 The methods employed by those who would gain a knowledge of 

 heterogenesis, cannot, from the very nature of the subject, be strict 

 laboratory methods ; but they are, none the less, methods similar to 

 those by which much other scientific knowledge has gradually been 

 built up. Those who work at this subject have to adopt methods 

 which, though carrying with them a greater element of certainty 

 and a larger amount of actual observation of the processes in 

 question, are fairly comparable with those employed by geologists 

 — we each of us strive to put the best and most reasonable inter- 

 pretation upon the facts that come under our observation, as much 

 as possible, irrespectively of preconceptions and a priori views.' 



In consequence of the sceptical attitude on the part of those 

 whose preconceptions hinder their working at such subjects for 

 themselves, it will be well for us now to look at the questions at 

 issue from a more general point of view. We find ourselves face 

 to face with two antagonistic doctrines : (i) the view that living 

 things no longer arise de novo, and (2) the view that living things 

 are still coming into being de novo both by Archebiosis and by 



' Those who are sceptical concerning Heterogenesis and have any desire to be 

 convinced may easily, by following my instructions, study the changes occurring 

 in Zoogloea masses in the pellicle on a hay infusion and the appearance of 

 Monads, Amoebae and Fungus-germs therein ; or they may study the origin of 



