285 



This statement is of particular interest as the colonies, when again trans- 

 ferred to the anorganic sulfur-chalk mixture, do not, or only very feebly, denitrify, 

 which means that they have almost or quite lost their power of chemosynthesis 1 ). 



This is not only true for the pure colonies separately, but likewise for the 

 combinations that may be made of them. Even when te whole bacterial mixture 

 on the plates is transported to the anorganic medium, only a slight or no chemo- 

 synthesis or denitrification at all occurs. On the thiosulfate plates the germs 

 preserve their autotrophy longer than on the broth plates, but there too, this, 

 power finally gets lost. The real cause of this loss is not yet quite explained. 

 With certainty it can only be said to take place when the concerned germs 

 augment when fed with organic food. 



Especially on the broth plates at 30 C. the colonies develop rapidly. It 

 seems that four or five species are thereby active. Three or four denitrify strongly 

 in broth bouillon with 0,1 to i% potassiumnitrate, and they predominate so much 

 that non-denitrifying species are not easily found. There is even no surer and 

 easier method to obtain bacteria denitrifying with organic food than this anor- 

 ganic denitrification, for although it is often difficult to isolate the active bacteria 

 from the organic denitrifications, this is here by no means the case 2 ). 



Among the colonies obtained from the anorganic mixture there are, as said, 

 some which do not denitrify with organic food. Probably they live in the sulfur- 

 chalk cultures as saprophytes at the expense of the organic matter formed by 

 the autotrophes. 



On silicic-thiosulfate nitrate-chalk plates develop, after two or three weeks, 

 yellowish colonies of i to i 1 /2 mm. in diameter and nearly i mm. high, evidently 

 autotrophic. In the anorganic mixture, freed from air by boiling, they cause a 

 vigorous denitrification after 24 hours at 28 C. already. When sown on broth- 

 gelatin the colonies appear to consist of two soft varieties 3 ) of B. stutzeri, which 

 do not melt the gelatin and of which one shows the usual structure; the 

 other, the commonest by far, lacks that structure completely, nevertheless it 

 resembles B. stiilzeri in the other cultural aspects. It consists of a white soft 

 mass of extremely small rodlets. In broth nitrate both show strong denitri- 

 fication, especially the soft form, so that it is one of the most intensely denitri- 

 fying bacteria I know. At reinoculation from the organic into the anorganic 

 food we also find here that the autotrophy and the power of anorganic denitri- 

 fication are lost. 



') In Untersuchungen iiber die Physiologic denitrifizirender Schwefelbakterien, 

 Sitzungsberichte Heidelberger Akademie. Biol. Abt. igi2, R. Lieske has come to 

 another result. 



-) The most important denitrifying soil bacterium, the spore-forming Bacillus nitroxus, 

 loses its denitrifying power quite or partly by growing on aerobic plates. Other species, 

 such as Bacterium pyocyaneum, B. stutzeri, B. denitrofluorescens preserve, in aerobic plate 

 cultures and in the collections, their denitrifying power unchanged for years. 



3 ) In reality there are three varieties, but the third which shows the character 

 of the ordinary tough, folded colonies of B. stutzeri, is rarer. It must be admitted 

 that the difference between the soft colonies and the typical B. stutseri is, super- 

 ficially, considerable, and I think that many other observers would bring them to 

 distinct species. 



