366 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



are especially suitable, or aniline-brown. After the staining, 

 'they must be dried and mounted in balsam in the usual way. 

 Photographs from specimens thus prepared show the most 

 delicate details, as, for instance, the flagella (Zeitschrlft fur 

 Mikroskopie, vol. i., p. 119). 



Measurement of the Diameter of the Flagella of Bacterium Termo. 



(A Contribution to the Question of the "Ultimate Limit of Vision" with our 



Present Lenses.) 



The Rev. W. II. Dallinger, already so well known for his 

 observations and studies of Monads, contributes a paper on 

 the above-named subject to the September number of the 

 Journal of the Royal Microscopical Society, full of interest, 

 but of which we can here give only a meagre outline. The 

 paper is illustrated with two fine plates, on one of which are 

 reproduced two of Dr. Koch's photographs, mentioned in 

 the preceding article. Bacterium termo is the smallest of all 

 the group, and although Kock, Warming, and others, had 

 detected the flagella on the larger specimens of other Bacte- 

 ria, they had never been seen on B. termo, though from anal- 

 ogy they were supposed to be present. The average length 

 of B. termo is about lu i 00 of an inch, and on this minute ob- 

 ject, by the most skilful manipulation of Powell & Lealand's 

 most recently improved objectives, and, also, with those of 

 Mr. Tolles, Mr. Dallinger and his coadjutor, Dr. Drysdale, 

 have not only succeeded in demonstrating the flagellum, but 

 have actually measured this line organic fibre, with the fol- 

 lowing results: (1.) The mean value of fifty measurements 

 made with the one-twelfth inch objective gives, for the diam- 

 eter of the flagellum, 0.00000489208. (2.) The mean value of 

 fifty measurements made with the one -sixteenth inch ob- 

 jective gives 0.000004886*73. (3.) The mean value of fifty 

 measurements made with the one-twenty-fifth inch objective 

 gives 0.00000488024. The mean value of fifty measure- 

 ments made with the one-thirty-fifth inch objective gives 

 0.00000488200. We thus get, for mean value of the whole, 

 expressed in vulgar fractions, tj o^ou of an inch ; so that we 

 may safely state that an atom of a semitransparent structure 

 uuiiVoo- * an i ,icn m diameter may become visible under 

 proper conditions of illumination and manipulation. 



