Boijal Microscopical Society. 269 



made, seemed inevitable. But nothing is more interesting to us 

 than to see how facts slowly and unceasingly pursued and ascer- 

 tained and collated, showed the inutility of our surmises. In 

 investigations of this kind we are convinced that sequences must be 

 made hj the facts themselves. Inference, however plausible, may 

 vitiate a whole train of observation; and, amongst other things, we 

 are bound to perceive the liability there must be to infer heterogeny 

 if observations be not long continued, and every transitional step 

 in the process be not demonstrated with the severest accuracy. 



To complete our work on this form we conducted a series of 

 heating experiments in precisely the same way as before. It will 

 suffice, therefore, to give the results of one series, which may be 

 taken as typical. 



Six slides were taken : a drop of the fluid put on and covered 

 with a thin cover. This was carefully examined, and if found to 

 contain what was needed was allowed slowly to evaporate. The 

 whole selected six were next slowly heated up to 250^ Fahr,, kept 

 at this heat for ten minutes, and then allowed slowly to cool. When 

 cold, they were carefully remoistened with distilled water — the 

 water flowing readily under the cover by capillarity — and they were 

 again examined and reported upon, 



Before they were put into the heating apparatus in each case 

 it was discovered that the elements required were there. 



On examination after heating, and immediately after fresh 

 moistening, nothing was visible but a baked amorphous mass. Two 

 hours after this no motion of any sort was visible, save in two, 

 where, with -^z^\ excessively minute points were seen to be in a 

 state of activity, which was translatory and not Brownian, 



Twelve hours after minute bodies — almost certainly known to 

 us as the very earliest motile form of the monad above described 

 after development from the germ — were seen in four of the fields. 

 These in two of the instances were traced up to full-sized monads 

 of the form and with the developmental history of the form at 

 which we were working ; whilst the other two on the second day 

 had many of the same in full maturity and complete action. The 

 other two were wanting in this form. 



From this it is clear that whilst in one condition this monad 

 can survive desiccation, in another — the true sexual-germ-state — it 

 can survive a temperature of 250° Fahr. 



We now heated another set of six under precisely similar con- 

 ditions up to 300° Fahr. But in this whilst some forms with 

 which we were acquainted survived by means of their germs, this 

 form was whollij destroyed, and not the trace of one in any form 

 could be discovered in any of the slides. 



