SOILS FERTILIZERS. 123 



"Provisionally we identify the detrimental organisms with the active pro- 

 tozoa of the soil, but as the zoological survey is yet incomplete we do not 

 commit ourselves to any particular organism or set of organisms or to any 

 rigid and exclusive definition of the term protozoa. 



"The increase in bacterial numbers following after partial sterilization by 

 volatile antiseptics is accompanied by an increase in the rate of ammonia 

 production until a certain amount of ammonia or of ammonia and nitrate has 

 accumulated, when the rate falls. Thus two cases arise: (1) When only small 

 amounts of ammonia and nitrate are present there is a relationship between 

 bacterial numbers and the rate of ammonia production, (2) when large amounts 

 of ammonia or of ammonia and nitrate are present there is no relationship. 

 The limit varies with the composition and condition of the soil. 



" Complications are introduced when the soil has been partially sterilized by 

 heat, because heat effects an obvious decomposition of the organic matter, thus 

 changing the soil as a medium for the growth of micro-organisms. The bac- 

 terial flora is also very considerably simplified through the extermination of 

 some of the varieties. These effects become more and more pronounced as the 

 temperature increases, and their tendency is to reduce the numbers of bacteria. 

 We find maximum bacterial numbers in soils that have been heated to the 

 minimum temperature necessary to kill the detrimental organisms (about 60°). 

 Both bacterial numbers and the rate of decomposition in such soils approxi- 

 mate to those obtaining in soils treated with volatile antiseptics, and the above- 

 mentioned relationships between these quantities also hold. 



"Although bacterial numbers are at a minimum in soils heated to 100° the 

 decomposition effected is at a maximum. 



"With this exception it is generally true that bacterial multiplication may go 

 on without increasing the rate of production of ammonia, but an increase in the 

 rate of production of ammonia does not take place without bacterial multipli- 

 cation. 



" The increase in bacterial numbers brought about by addition of bacteria 

 from the untreated soil into partially sterilized soil leads to still further pro- 

 duction of ammonia and nitrate unless too large a quantity of these substances 

 is already present. But the subsequent depression in bacterial numbers conse- 

 quent on the development of the detrimental organisms is generally (though 

 not always) without effect on the rate of decomposition, apparently because it 

 does not set in until too late." 



The complexity of the micro-organic population of the soil, B. J. Russell 

 (Science, a. ser., SI {1913), No. 953, pp. 519-522).— This article contains a re- 

 statement of the author's conclusions regarding the relation of protozoa to bac- 

 terial activity in the soil and a reply to recent papers by other investigators 

 (E. S. R., 27, p. 620; 28. pp. 323, 324, 719) taking issue with them. Recognizing 

 fully the complexity of the soil fertility problem, the author reiterates his claim 

 that destructive organisms are an important factor, although not the only one 

 involved in the matter. 



A method for the determination of the number of Protozoa in soils, O. 

 R.\iiN (Ccnthl. Bald, letc.^, 2. Abt., 86 (1913). No. 15-18, pp. .',19-.'i21) .—The 

 method, which is a dilution method, is briefly described, and examples of results 

 obtained by its use are given. 



Chemical weathering- of silicates and rocks with special reference to the 

 influence of humus substances, H. Niklas (Chemischc Verivitterung der Sili- 

 kate unci der Gesteine mit hesonderer BerucJcsichUgung des Einflusses der 

 Hiimiifi.sfolfe. Vienna, Berlin, and London, 1912, pp. XX+l-iS; rev. in Natunv. 

 Ztschr. Forst u. Landw.. 10 (1912), No. 11, pp. 559, 560). — This paper reports 

 96700°— No. 2—13 3 



