20 



SCIENCE. 



[N. S. Vol. Vir. No. 158. 



suitable to the nourishment of plants have 

 been the subject of investigation in many 

 quarters. It has been established with a 

 considerable degree of certainty that the 

 nitrifying organisms are capable of existing 

 on the surface and even to a considerable 

 depth in the interior of bare rocks at high 

 altitudes where even the mosses and lichens 

 fail to grow. It is evident, therefore, that 

 these organisms have a great deal to do in 

 the incipient stages of vegetable life and in 

 the preparation of the first particles of 

 humus, which is the substance distinguish- 

 ing soil from finely cominuted rocks. Later 

 investigations show also that nitrogen exists 

 in combination with metals, as metallic 

 nitrids, as has been shown by the investi- 

 gations of Hillebrand and others. Among 

 other metallic nitrids that of thorium has 

 been detected. Notable quantities of min- 

 eral nitrogenous compounds have been 

 found in the carnallit coming from the 

 Stassfurt mines. As much as .018 per 

 cent of ammoniacal nitrogen has been 

 found in these salts. The artificial carnal- 

 lit is richer in ammonia than that of nature. 

 It is evident that in carnallit the ammonia 

 replaces a small portion of the potash. 



In regard to the origin of this am- 

 moniacal nitrogen, it is generally under- 

 stood that it comes from the decomposition 

 of the living beings which peopled the sea 

 whose evaporation produced the saline de- 

 posits. The ammoniacal nitrogen which is 

 present in the primitive rocks, however, 

 cannot be ascribed to this source, since these 

 rocks were formed at an epoch when life 

 did not exist upon the surface of the earth. 

 This ammoniacal nitrogen, as has been said, 

 occurs almost uniformly as metallic nitrids. 

 It was doubtless, therefore, the first form 

 of nitrogen used to nourish the beginnings • 

 of animal and vegetable life, since it existed 

 before any of these forms could, hj their 

 decomposition, have furnished available 

 nitrogen for plant growth. This am- 



moniacal nitrogen, therefore, must have 

 served directly to nourish the first forms of 

 life and thus to have helped lay the founda- 

 tions of the whole vegetable world. (I'En- 

 grais, Mar. 12, 1897 ; Apr. 9, 1897.) 



A heated discussion has arisen between 

 the French and German schools of agricul- 

 ture in regard to the harmfulness of the 

 denitrifying organisms found in soils and 

 manures. Wagner urges the importance of 

 sterilizing stable manure in order to prevent 

 the loss of nitrogen that would otherwise be 

 brought about by the organisms contained 

 in it. Deherain, on the other hand, declares 

 that this precaution is unnecessary when 

 stable manure is applied to ordinary soils 

 in the usual quantities. 



Comparatively little attention has been 

 given to the isolation and study of pure 

 cultures of the nitrate-destroying organisms 

 found in soils, manures, straw and fodders. 

 While their existence has been repeatedly 

 proved and their behavior in mixed cultures 

 has been studied by Gayon and Dupetitf 

 Springer, Deherain and Maquenne, Breal 

 and others, the first denitrifying organisms 

 obtained in pure cultures and accurately 

 described were those reported by Burri and 

 Stutzerin 1895. These investigators found 

 a denitrifying organism in horse manure 

 which they called Bacillus denitrificans I.f 

 and which they found to rapidly destroy 

 nitrates when growing in the same culture 

 with B. coli communis. They also isolated 

 and described, under the name of B. deni- 

 trificans II., a denitrifying organism from 

 straw. 



A second denitrifying organism was found 

 in horse manure by Schirokikh early in 

 1896, while more recently an organism of 

 this class was found in cow manure by 

 Ampola and Garino. 



Considerable progress in our knowledge 

 of the denitrifying ferments in soil has 

 been made by Ewell in the Division of 

 Chemistry, Department of Agriculture, in 



