ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 485 



With B.Jiuorescens a distinct cloudiness is present under the niveau, 

 ■which is separated by a sharp clear zone ; there is also a cloudiness above 

 the niveau, but this is feeble after 30 days. 



With B. subtil is there is formed at first a niveau with a very slight 

 underlying cloudiness, the clear zone not being well marked ; the niveau 

 soon disappears, and flocculi, consisting of sporulating threads, appear in 

 the fluid. 



The authors never observed double niveaus. They found, as 

 Beijerinck had seen, that the niveaus develop first in the lower strata 

 in the neighbourhood of the nutrient material and then rise slowly, but 

 that after 9-12 days they begin to sink again. Sharp niveaus are seen 

 to form only with motile varieties. The niveaus appear where the 

 amount of underlying nutriment and overlying oxygen form an opti- 

 mum for the bacterial development. By pipetting off samples at 

 different levels and making plates, they showed that the number of 

 bacilli were much greater in the niveau than in the cloudiness above or 

 below ; thus in the case of B. typhi the average for three observations 

 showed 2 colonies from the upper cloudiness, 43 colonies from the niveau, 

 and 23 from the underlying cloudiness ; and for B. coli 2, 100, and ;">7 

 respectively. 



Comparative Study of Sixty-six Varieties of Gas-producing Bac- 

 teria found in Milk.* — F. C. Harrison finds that the gas-producing 

 bacteria of milk belong to a large group of organisms, consisting of 

 varying sized rods with rounded ends, that stain unevenly and are 

 decolorised by Gram ; they grow well on ordinary media at room tern 

 perature, better at 37° C. ; they do not liquefy gelatin ; they produc* 

 acid in milk, which is usually coagulated ; they are potential anaerobes 

 reduce nitrates and ferment lactose, glucose, and other saccharoses. Severai 

 are typical B. coli and B. lactis aerogenes, and between these extremes 

 there are manifold varieties. The author attempts to classify these into 

 seven groups. He found that the neutral red test was of no value in 

 separating the members of the coli group, and the agglutination test was 

 only of limited value in diagnosing closely related varieties of B. coli 

 and B. lactis aerogenes. The percentage of gas-producing forms to the 

 total bacterial content of milks varied from a fraction of 1 p.c. to 31 ' 8 

 p.c. ; the organisms probably came from manure, flies, and in some cases 

 from the udder of the cow. Gas-producing bacteria tainted cheese, and 

 the coloured cheeses gave the appearance known as " mottled," which is 

 probably the result of the bleaching action of the gases generated. 



Bacillus Involutus.t— L. Waelsch describes the bacterial aspects of 

 an organism obtained from non-venereal preputial secretion. On glyce- 

 rin-agar and gelatin-agar plates inoculated with smegma, there appeared 

 after 24 hours shining dew-drop colonies the size of millet seeds ; these 

 were round, sharply ^contoured with toothed margins, and contained 

 strongly retractile granules, which were seen to consist of short rods 

 lying in various directions. The rods were of various sizes and shapes, 

 with rounded ends, and showed extraordinary involution forms ; they 



• Centralbl. Bakt., 2< e Abt. xiv. (1905) pp. 349 and 472. 

 t Centralbl. Bakt., l ,e Abt., xxxviii.(1905) p. 645. 



