INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 837 



Classification of Bacteriacese.* — In a general review of our state 

 of knowledge of tlie Schizomycetes, Dr. Luersscn arranges the genera 

 of BacteriacenB as follows : — 



I. Cells not united into filaments, sejiarating immediately after 

 division, or in couples, free or united into colonies (Zoogloea) 

 by a gelatinous substance. 



A. Cells dividing in one direction only. 



a. Ccdls globular : Micrococcus. 



p. Colls elliptical or shortly cylindrical : Bacterium. 



B. Cells dividing regularly in three directions, and thus 



forming cubical families, having the form of 

 packets strung crosswise, and consisting of 4, 8, 

 16, or more cells : Sarcina. 

 II, Cells united into cylindrical filaments. 



A. Filaments straight, imperfectly segmented. 



a. Filaments very fine and short, forming rods : 



Bacillus. 

 (3. FiLiments very fine and very long : Leptothrix. 

 y. Filaments thick and long : Beggiatoa. 



B. Filaments wavy or spiral, 



a. Filaments short and stiff. 



a. Filaments slightly wavy, often forming 



woolly flocks : Vibrio. 



b. Filaments spiral, stiff, moving only for- 



wards or backwards : Spirillum. 

 (3. Filaments long, flexible, with rapid undulations, 

 spiral through their whole length, and en- 

 dowed with great mobility : Spii-ochcete. 

 A diagnosis follows of each species, with an account of what is 

 known of its structure and habits, and of its physiological role. 



Atmospheric Bacteria. t — Continuing the observations contained 

 in a previous paper, | which did not deal with Bacteria, M. Miquel has 

 succeeded in counting tlic spores of bacteria, and while couflrming 

 M. Pasteur's observations that they are always present in the air, 

 shows that their number is subject to incessant variations. 



Very small in winter, the number increases in spring, is very high 

 in summer and autumn, then sinks rapidly when frost sets in. This 

 law also applies to spores of fungi ; but while the spores of moulds 

 are abundant in wet periods, the number of aerial bacteria then 

 becomes very small, and it only rises again in drought when the 

 spores of moulds become rare. Thus, to the maxima of moulds 

 correspond the utinlma of bactia-ia, and reciprocally. 



In summer and autumn, at Paris, lOUO germs of bacteria are 

 frequently found in a "cubic metre of air. In winter the number not 

 tincouimonly descends to four and five, and on soini! days tlio " dust " 

 from 2U0 litres of air proves iiicai)ablo of causing infection of the 



♦ ' Rev. Iiiternat. Sci..' iii. (1S80) p. 242. 

 t ' CompU's Kendiis,' xci. (1880) p. 04. 

 X See tliis Juurnal, i. (1878) p. 1U2. 



