ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 705 



Engelmann's Bacterium - Method. * — Dr. T. W. Engelmann 

 replies to various objections to his bacterium-method for detecting 

 the evolution of oxygen, j especially those of Pringsheim,| and points 

 out the limits to the use of the method, which cannot be applied to 

 the quantitative determination of the oxygen evolved. He further 

 describes the conditions most favourable for the employment of the 

 process. 



The drop must contain only a single kind of bacterium, and must 

 therefore be taken from a pure culture. The best results are obtained 

 with a bacterium of high oxygen-requirement. The bacteria should 

 be neither too large nor too small ; cocci of 1-2 //, diam., or rods 2-3 /a 

 in length and about 1 /* in diam. afford the best results. The number 

 of individuals of the bacterium must be large enough for them to 

 collect rapidly round the source of oxygen ; the drop should appear 

 slightly turbid to the naked eye. During observation, evaporation 

 must be carefully prevented from the margin of the cover-glass. 



Solid Nutritive Media for Bacteria.§ — M. E. de Freudenreich 

 compares Dr. Hesse's apparatus, for testing for Bacteria in the 

 atmosphere, with that of Dr. Miquel, of Montsouris. In the former 

 case, air is drawn through a tube lined with gelatin ; in the latter 

 method the air is passed through water and then distributed in drops 

 to a series of tubes containing sterilized broth. The advantage in 

 this latter method lies in the fact that, when any alteration is observed 

 in th c broth in any one tube, this tube can be examined ; whereas in 

 Hesse's method, in order to examine a single colony the whole 

 apparatus has to be exposed to the atmosphere, and disturbing con- 

 ditions may occur ; and although as a rule Bacilli develope on the 

 spot on which they fall, yet not unfrequently, and especially during 

 summer, they may spread so rapidly that the whole of the gelatin 

 becomes liquid. 



The author undertook numerous comparative experiments with 

 the two methods. Out of a series of seven experiments, undertaken 

 at the same time and place, and using peptonized gelatin in the one 

 apparatus and peptonized beef broth in the other, he obtained the 

 following results : Four were more favourable to the liquid medium 

 (that is more bacteria were found by this method than by the gelatin 

 method, in the same volume of air) ; one was favourable to the solid 

 medium ; two gave identical results with the two media. The 

 author, therefore, concludes in favour on the whole of Dr. Miquel's 

 method ; but adds that Dr. Hesse's is not to be neglected, on account 

 of the ease of transport and manipulation of his apparatus. 



Cultivation of Comma-bacilli. |] — Dr. F. Hueppc has obtained 

 very interesting results as to the spores of the cholera bacillus by slide- 

 cultures, which during the observations were kept at a temperature of 

 34°-37° C. on a hot stage. The slides used were hollow ground, so as to 



* Bot. Ztg., xliv. (1886) pp. 43-52, 64-9. 



t 8ee this Journal, i. (1881) p. 962. J Ibid. 



§ Arch. Sci. Phys. et Nat., xv. (1886) pp. 105-20. 

 j| Fortschr. d. Med., iii. (1885) p. 619. 

 Ser. 2.— Vol. VI. 3 A 



