540 SUMMARY OF CURRENT RESEARCHES RELATING TO 



denitrification may be caused by exclusion of air, and the same holds 

 good in regard to the soil. 



Nitrogen-fixing Bacteria.* — Gerlach and Vogel have made fresh 

 observations on the relation between a supply of organic material 

 (grape-sugar, calcium propionate, &c.) and the fixing of free nitrogen 

 by soil bacteria. The bacterium used was Azotobacter chroococcum, and 

 it was found that an increase of grape-sugar up to 12 grin, per 1000 

 led to an increase of nitrogen fixation, but above that amount an 

 increase in sugar led to a decrease in the activity of fixation. Their 

 further work is a consideration of the results obtained by Beijerinck 

 and van Delden in their work on nitrogen-fixing bacteria. 



Culture of the Nitroso-Bacterium.f — H. S. Fremlin finds that a 

 practically pure culture of the nitroso-bacterium can be obtained after 

 sub-culturing for seven months in Winogradsky's ammonia solution, 

 which consists of water containing 1 per 1000 ammonium sulphate, 

 1 per 1000 potassium phosphate, and 1 per 100 magnesium carbonate. 

 The bacterium will grow in this solution in the presence of organic 

 matters such as are contained in peptone beef broth, Witte's powdered 

 peptone, and urea. The author also shows that the bacterium will grow 

 not only on silica jelly but also in any ordinary organic medium. 



/Motility of Rhizobium.f — Albert Schneider continuing his investi- 

 gations of the leguminous tubercle bacteria, states that he has now dis- 

 covered that when the Ehizobia of sweet clover are transferred to acid 

 media they become much smaller and more uniform in size, and move 

 with a rapid, jerky, to and fro, and rotary movement. To the bacterium 

 from this clover he gives the name of R. mutabile, a species which he 

 believes will prove to be the chief or dominant type as it occurs in the 

 tubercles of the greater number of leguminous plants. In neutral 

 media the organism remains non-motile. 



Observations on Sarcina, Streptococcus, and Spirillum.§ — David 

 Ellis has made a long and very complete series of comparative morpho- 

 logical and physiological observations on Sarcina urm Beijerinck, 

 Streptococcus tgrogenus Henrici, and Spirillum giganteum Migula. 



New Group of Sulphur-Bacteria. || ■ — A. Nathansohn describes a 

 new group of sulphur-bacteria observed by him in sea-water to which 

 potassium sulphide had been added, and which had been infected with 

 Beggiatoa-like organisms. They were afterwards cultivated and studied 

 in sea-water with the addition of 0*1-1 p.c. sodium thiosulphate or 

 some similar medium ; no organic food was necessary. A large number 

 of forms of this group were isolated by means of plate cultures, but 

 in this paper their metabolism only is described. The organisms were 

 unable to develop in the absence of C0 2 , but they were unable to 

 oxidise such substances as glucose, though these organic substances had 

 no ill-effect on their growth. It would seem that in these curious 



* Centralbl. Bakt., ix. (1902) pp. 817-21 and 8S1-92. 



t Proc. Roy. Soc, lxxi. (1903) pp. 356-61. 



X Bot. Gazette, xxxv. (1903) pp. 56-8. 



§ Centralbl. Bakt., xxxiii. (1903) pp. 1-23, 81-96, 161-66 (2 pls.\ 



|| Mittheil. Zool. Stat. Neapel, xv. (1902) pp. 655-80. 



