BACTERIA FIXING ATMOSPHERIC NITROGEN 109 



Morphology of the anaerobic bacteria. 



CI. pastorianwn is an actively motile gram-positive rod, occurring singly. 

 The straight cylindrical rods, with rounded ends, are, when young, 1.5 to2/ilong 

 by 1.2 to 1.3/u thick. They may reach a size of 2 to 6 by 0.8 to 1.3,u. The proto- 

 plasm is homogeneous, stains well with aniline dyes and gives a yellow color with 

 iodine; older cells become spindle-shaped, coloring violet-brown with iodine. 

 The size of the cells is greatly influenced by the composition of the medium. 

 Both young and old cells are motile, by peritrichous flagella. When the nutrients 

 in the medium are exhausted, spore formation takes place; the rods change into 

 short, thick cells greatly swollen in center, with a diameter twice, or more than 

 twice as great as the original. The cell membrane becomes sharply contoured 

 and surrounds an hyaline substance which encloses the spore. The contents 

 of the cell become granulated, stain with aniline dyes only with difficulty and 

 color violet with iodine. The spore is formed in one end of the enlarged part of the 

 cell and stains well with aniline dyes, but not with iodine; methylene blue stains 

 the spore dark blue and the protoplasm light blue. By the swelling of the hyaline 

 substance, the mother cell bursts open in one end: the ripe spore, 1.6 by 1.3^, is 

 now found to lie in a rounded three cornered spore-capsule. It is characteristic 

 of the species for the capsule to adhere to the spore for a considerable period of 

 time. Under favorable conditions, as on fresh media, the spores swell up and the 

 spore envelope breaks. The spore-germination takes place at one pole towards 

 the open end of the capsule. The young cell soon divides, while the old shell may 

 remain in the liquid for a long time. The cell also produces various involution 

 forms, as long threads irregularly swollen and often carrying a spore at one end. 

 Glycogen and granules accumulate in the cells of the organisms just previous to 

 spore formation. 



Bredemann 28 included all the butyric acid bacteria under the name of 

 Bac. amylobacter A. M. et Bred., since the various characteristics, such 

 as size and shape of organism, motility, character of growth on various 

 media, liquefaction of gelatin, carbon sources, products of metabolism, 

 deposition of amylaceous material are all variable characteristics. The 

 most stable characteristics are the form and size of spore as well as the 

 polar germination. Omeliansky, 29 however, did not agree with the 

 grouping of all the Clostridia, Granulobacter, Bac. orthobutylicus and 

 others together, but suggested that some of the characters are sufficiently 

 constant to be of value in classification. 



The nitrogen-fixing capacity is well distributed among the butyric 

 acid bacteria, including the CI. pastorianum of Winogradsky, CI. 



23 Bredemann, G. Untersuchungen fiber die Variation und das Stickstoffbin- 

 dungsvermogen des Bacillus asterosporus A. M. Centrbl. Bakt. II, 22: 44-89. 

 1908; 23: 385-568. 1909; Ber. deut. bot. Gesell. 26: 362 and 795. 1908. 



29 Omeliansky, W. L. Morphological and cytogical investigations on nitrogen- 

 fixing bacteria (Russian). Arch. Sci. Biol., 20: 24-49. 1916. 



