MICROSCOPY. 361 



Theoretical Limit of Aperture. 



In an able paper on the Theoretical Limit to the Apertures 

 of Microscopical Objectives, Professor G. G. Stokes, D.C.L., 

 etc., after alluding to Professor R. Keith's elaborate compu- 

 tation relative to Tolles's one -sixth microscopic objective, 

 which is given in full in the Journal of the Royal Micro- 

 scopical Society, July, 1878, and fully endorsed by him, 

 states that the reason for scepticism as to the results of such 

 calculations seems to be a notion derived from a priori con- 

 siderations, that it is impossible to collect into a fucus a pen- 

 cil of rays emanating from a radiant immersed in water or 

 balsam of wider aperture than that which in such a medium 

 corresponds to 180 in air, or, in other words, than twice the 

 critical angle ; and this he disproves by showing that in cer- 

 tain particular instances it is untrue, so that the aperture in 

 the case of a medium with a refractive index 1.525 may, at 

 the extreme, exceed the supposed limit by over 16. 



MICRO-ORGANISMS, BACTERIA GERMS, SPORES, ETC. 

 Anaerobiosis of Micro -organisms. 



M. Gunning, in a note read July 1, at the French Acad- 

 emy, states that he has repeated his experiments on Anaero- 

 biosis, or life without oxygen, under conditions to which no 

 exceptions can be taken, and proves conclusively that such 

 life is impossible. 



Admitting the practical impossibility of obtaining spaces 

 where the absolute absence of oxygen could be proved, he 

 used glass flasks, hermetically sealed, in which as large quan- 

 tities as possible of putrescible matter were placed in con- 

 tact with the smallest possible quantities of oxygen. The 

 details of his mode of doing this are published in the An- 

 nals of the Academy of Sciences, Amsterdam, vol. xii., 1878, 

 and in the sixth part of the Journal of Practical Chemistry. 

 He found that w 7 hen the flasks were sealed and exposed to a 

 temperature of 38 to 40, putrefaction was immediately es- 

 tablished to be definitely arrested, however, in all the flasks 

 after a longer or shorter period ; often very short, but always 

 sensibly proportioned to the quantity of oxygen supposed 

 to be present. After two years some of these flasks had lost 



Q 



