SUPPLEMENT 75 



column of each series are given the lowest percentages which merely retard 

 development, and in the second the doses which completely inhibit it. The 

 symbol > signifies ' more ', but not much more than the number following 

 (comp. also BOULLANGER and MASSOL, 1903, 1904). We may deduce several 

 important conclusions from this table : 



i. The various organic substances are by no means neutral to the nitro- 

 bacteria, but really operate directly as antiseptics, and their effect is not less 

 intense than that of carbolic acid on ordinary Bacteria. 



11. 30-56, for All these facts . . . nitric acid, read Hence one would conclude 

 that nitrate formation always began to take place in nature after the whole of 

 the ammonia had been used up in nitrite manufacture. As a matter of fact, 

 however, we always find nitrite and nitrate formation going on in the soil at 

 the same time. This suggests that the ammonia has an injurious effect only 

 on the development of the nitrate Bacteria and that the full-grown cells are much 

 less sensitive to its influence (BOULLANGER and MASSOL, 1904). We must leave 

 undiscussed the question as to whether the activity of the nitrite Bacteria 

 begins to manifest itself markedly only after the organic substances (dead 

 animals and plants, excreta) have been completely broken down by the 

 ordinary fermentative forms so that their carbon has been transformed into 

 CO 2 and their nitrogen into NH 3 or N (LOHNIS, 1904). A clearly marked separa- 

 tion of nitrification from fermentation might indeed have special significance, 

 since otherwise the nitrates formed would not become of service to green 

 plants, but rather be broken down by the fermentative Bacteria which denitrify 

 such bodies. 



In this relation it should further be noted that the nitro-bacteria do not 

 exhibit their activities merely in arable soils where ammonia is presented to 

 them as a result of manuring, but that they also occur at the sea-bottom, where 

 THOMSEN (1907) has shown the nitrite formers at least are generally distributed ; 

 he shows, however, that the nitrate Bacteria occur only near the coast-line. 

 Further, as WINOGRADSKY has already clearly demonstrated, the nitro-bacteria 

 also can establish themselves on bare calcareous rock. In such situations they 

 are able to transform into nitric acid the small quantities of combined nitrogen 

 brought to them in rain. They also decompose the lime and thus render the 

 rocky substratum available for higher plants. Nitro-bacteria are thus the first 

 colonists of calcareous rock, and so organic material is constructed by nitrate 

 Bacteria entirely independently of light and of other organisms. Since ammonia 

 is in reality always produced by organisms, that substance is not available for 

 the nitrite formers ; quantities of nitrite formed in the air by electric discharge 

 are, however, at the disposal of the nitrate formers. 



If now, having disposed of the nitro-bacteria, we glance back at the pheno- 

 mena we met with in connexion with the colourless sulphur-bacteria, these 

 show themselves in an entirely new light. Not only do we see a perfect analogy 

 between the respiration of NH 3 on the one hand, and of SH, on the other, but 

 we are led to reconsider the poor results obtained by feeding Beggiatoa with 

 organic substances. It is in the highest degree probable that the sulphur- 

 bacteria are also autotrophic organisms (WINOGRADSKY, 1890, p. 275), and 

 that they thrive even better when organic food- stuffs are entirely excluded than 

 when supplied with ' bad ' nutrients. One can only wonder why this research 

 was not carried out long ago. NATHANSOHN has shown in relation to the 

 Bacteria that oxidize thiosulphate, that they exhibit a continuous increase in 

 their dry weight when in the presence of CO 2 only and when organic substance 

 is absent. Further, NATHANSOHN has also succeeded in proving that the 

 addition of organic material is of no service to these Bacteria and in no way 

 acts as a substitute for CO 2 . Here also we have to deal with obligate auto- 

 trophic forms. The energy required for the further working up of CO,, and 



