214 SUMMARY OF CUREENT RESEARCHES RELATING TO 



lactose and are indifferent to other sugars ; those of the second group 

 act on lactose and on dextrose : those of the third group act on lactose,, 

 dextrose, and on mannite. 



Lactic Acid Bacteria (type Giintheri) from Various Sources.* — 

 L. Miiller finds that the different strains of B. (jiiMlieri show marked' 

 cultural and morphological differences, and have but little conformity 

 in their relations to the various carbohydrates. The cultural properties 

 and the power to form acid from sugars is the same with both B.giintlieri 

 and Streptococcus agalactia. ; under certain cultural conditions the strepto- 

 coccus is morphologically indistinguishable from the bacterium, which 

 also not infrequently takes a streptococcal form. 



Form and Structure of Bacterial Colonies.! — H. B. Hutchison 

 finds that the form of colonies lying deeply in a medium is dependent 

 on the elasticity, cohesion, and superficial tension of the medium. The 

 constitution of the superficial colonies depends especially on the cohesion 

 of the growing cells and the surface of the medium. If the growth is 

 accompanied with a secretion of slime, the colonies assume a spherical 

 shape and shining appearance. If the cells in the centre of the colony 

 lose their energy or die whilst the cells at the periphery continue to 

 grow, a flattened growth results. The property of taking up water from 

 the medium by the growing organism has also an influence on the shape 

 of the colony, and on the motility of the bacteria. The growth of 

 colonies, and the pigment formation, mor]ihology and physiology of the 

 cells, are influenced by light and air and by changes of temperature. 

 The construction of the colonies depends not only on a regular an-ange- 

 ment of the cells, but on the constitution of the cell plasma. 



Mutation of Bacteria. | — R. Massini has observed a bacillus which 

 gave colourless colonies on Endo's medium ; by making repeated sub- 

 cultures on Endo plates from one-day-old colonies, only colourless 

 colonies were obtained, but if subcultures were made from three-day-old 

 colourless colonies, the Endo plate showed both colourless and red 

 colonies ; these red colonies in subculture always formed red colonies. 

 The author regards this as an instance of bacterial mutation, and has 

 named the organism B. coli nmiahiUs. 



Nitrogen Bacteria.§ — H. Fischer considers that on morphological 

 grounds, Asotohacter holds an intermediate position between Strepto- 

 coccus and Sarcina, and should not on physiological grounds alone be 

 regarded as a distinct species. The chief physiological character of this 

 organism is that of fixing atmospheric nitrogen, so that it is able to 

 develop in a medium that is completely free from nitrogen (nitrates, 

 etc.). It grows well in media containing • 1 p.c. potassium nitrate, and 

 less well with ammonium sulphate, and with pepton • 1 p.c. only slight 

 growth ; it grows badly, or not at all, on gelatin : on limited supply of 



• Centralbl. Bakt., 2te Abt., xvii. (1907) p. 713. 

 + Op. cit., 2te Abt. xvii. (1906) p. 593. 



X Verein. Mikro., Berlin, 1906. See also Centralbl. Bakt., Ite Abt. Orig., xxxviii, 

 (1906) p. 98. 



§ Verhandl. Naturhist. Vereins.'Boun, 1905, p. 185. 



