5° 



PHYSIOLOGY OF NUTRITION 



Depth in the Black Sea, 

 meters 



215 



432 



2040 



2525 



H 2 S Context per 100 l. 

 cc. 



33 

 222 



555 

 655 



In the mud of the sea-bottom are therefore going on various kinds of fermenta- 

 tion, which are accompanied by the elimination of hydrogen sulphide." Only 

 because of the presence of sulphur bacteria is the hydrogen sulphide prevented 

 from reaching the upper layers of water. 



Nitrifying and sulphur bacteria use ammonia and hydrogen sulphide, which 

 are injurious to other organisms, and aid in preventing the accumulation of these 

 substances upon the surface of the earth; oxidizing them to nitric and sulphuric 



Fig. 30. — Part of a membrane of sulphur bacteria, magnified n times. (After Yegunow.) 



acids, they bring these substances again into the general circulation of materials 

 in nature. 



Besides ammonia and hydrogen sulphide, hydrogen is also produced in 

 large amounts by the decomposition of complex organic compounds, and yet 

 it is present only in minimal quantities in the atmosphere. According to various 

 determinations, the amount of hydrogen in the air varies between 0.0003 an d 

 0.0 1 per cent. It therefore appears that processes must occur on the earth, 

 by which hydrogen is combined and so started anew in the general circulation 

 of materials. 



The researches of Kaserer 1 have shown that there are special bacteria that 

 utilize hydrogen. Viewed from the standpoint of thermo-chemistry, hydrogen 

 represents the best nutrient substance. Its heat of combustion is eight times 

 that of starch; a gram of starch gives out during combustion but 4.0 kg.-cal., of 

 heat, while a gram of hydrogen gives out 34.6 kg.-cal. (see page xxviii). Certain 

 soil bacteria, such as Bacillus pantotrophus and Bacillus oligocarbophilus, 



1 Kaserer, Hermann, Die Oxydation des Wasserstoffes durch Mikroorganismen. Centralbl. Bakt. // 

 16: 681-696, 769-775. 1906. Lebedeff, A. F., Ueber die Assimilation des Kohlenstoffes bei wasserstoff- 

 oxydierenden Bakterien. Ber. Deutsch. Bot. Ges. 27: 598-602. 1909. Nabokich, A. J., and Lebedeff, 

 A. F., Ueber die Oxydation des Wasserstoffes durch Bakterien. Centralbl. Bakt. 11, 17 : 350-355- 1907. 



" This deduction is of course not strictly accurate; although perhaps most of the hydrogen 

 sulphide, ammonia and hydrogen in nature is of organic origin, these substances are also pro- 

 duced, to some extent at least, quite independently of organisms. — Ed. 



