58 TJie Angular Aperture of Ohjedives. 



is secured, and so far at least as adult forms go, we are prepared, 

 as a general rule, to accept it. We question its application to 

 sporules, where tbey exist ; and nothing but patient inquiry and 

 experiment on these, as such, can definitely settle the question. 

 But the unequal diffusion of heat from causes known and unknown, 

 must always in individual experiments cause variety of results. 

 Cohn himself confirms the fact that Bacteria are not always killed 

 by hoiling in flasks, and that Bacillus suhtilis (the lactic acid 

 ferment organism) survives the boiling of the solution in which it 

 is contained ; and that in every case the boihng should be continued 

 for an hour. 



We think that the above experiments justify us in questioning 

 the statement of a recent partisan of Abiogenesis, " that even if 

 Bacteria do multiply by means of invisible gemmules, as well as 

 by the known process of fission, such invisible particles possess no 

 higher power of resisting the destructive influence of heat than the 

 parent Bacteria themselves possess."* This may be true of Bac- 

 teria, but it certainly remains to be proved ; while its inapplicability 

 to all sporules is apparent. 



II. — The Angular Aperture of Ohjedives. 



By Egbert B. Tolles, U.S.A. 



Any objective when adjusted to the maximum point and measured 

 in air, having less than 180° angular aperture, such objective, 

 being applied in the microscope to observation of an object in the 

 ordinary balsam slide, necessarily has less than 82^ of aperture 

 practically for that balsamed object. Now, avowedly English 

 objectives, and presumptively all of single-lens fronts of common 

 crown glass, are of rather less than 180'^ air angle. Therefore it 

 is evident that I did not " challenge " test of English objectives as 

 against any other whatever built on that plan. There was nothing 

 invidious in my remark, and fairly considered I think not any such 

 appearance. It was cautionary merely. Thus (as stated in my 

 note, which happened to follow Mr. Wenham's in your last issue) 

 I obtained a view with definition of a fine object unquestionably 

 with the advantage of a pencil of above 100° of actual practical 

 balsam angle, measured with the object in focus at the 7noment. 



Well, measured in air, this objective would show not distin- 

 guishably more than any English (or other) objective of the ordi- 

 nary construction corrected for air angle approximating 180°. In 

 Mr. Wenham's tank in balsam a proper difference would be shown 



* Bastian, ' Proc. Koy. Soc.,' March, 1873. 



