60 



SOIL FERMENTS IMPORTANT IN AGRICULTURE. 



By Dr. W. H. Wiley, Chief of the Division of Chemistry, U. S. 

 Department of Agriculture, in Year Book of U. S. Dept. of 

 Agriculture for 1895. 



( Continued ). 



PRECAUTIONS IN SAMPLING. 



First of all, the method of sampling must be such as to secure for ex- 

 amination portions of soil which certainly contain no other organisms 

 than those locally found therein. The methods of securing the samples 

 are purely technical, and will be fully described in a special bulletin from 

 the Division of Chemistry of the Department of Agriculture. 



THE CULTURE SOLUTION. 



Many readers of these pages who are not bacteriologists will be in- 

 terested in knowing the character of the solution which is used for testing 

 the nitrifying vitality of the ferments in the soil. A solution which we 

 have found very useful for this purpose is composed of the following con- 

 stituents ; Potassium phosphate, one gram ; magnesium sulphate, half 

 a gram ; ammonium sulphate, two-tenth gram ; calcium ohloride, a 

 trace, and calcium carbonate in excess of the amount which will be neces- 

 sary to combine with all the nitric acid produced from the ammonium 

 sulphate present. The above quantities of materials are dissolved or 

 suspended in one litre (about one quart) of water, and one-tenth of this 

 volume is used for each culture solution. This quantity is placed in an 

 Erlenmeyer flask, which is then sterilised, after stoppering with cotton, 

 by being kept at the temperature of boiling water for an hour on three 

 successive days. The flask itself before using, should be thoroughly 

 sterilised by heating to 300 deg. F. for on hour. 



The calcium carbonate employed in the above culture solution should 

 not be prepared by finely grinding marble or chalk, but in a chemical 

 way by precipitation. It is best thoroughly sterilised separately and then 

 added to the flask immediately before seeding. The sterilized spoon 

 which is used for seeding, holds, approximately, half a gram of the soil. 

 This spoon is filled from the contents of one of the freshly opened sample 

 tubes, underneath a glass hood, the plug of cott«n is lifted from the 

 sterilized flask, and the contents of the spoon quiakly introduced and the 

 plug of cotton replaced. While the above details are well known to the 

 bacteriologist, they are not appreciated, as a rule, by the general reader. 

 From the numerous inquiries concerning this process which have been 

 received at the department, it is believed that the above brief outline of 

 the method of procedure of securing samples of soil and seeding sterilized 

 solutions therewith will be useful. 



NOTING THE PROGRESS OF NITRIFICATION. 



It will be seen from the above description that the object of the tests 

 in question is to determine the activity and strength of the nitrous and 

 nitric organisms alone, inasmuch as the process begins with an am- 

 moniacal salt. At the end of five days from the time of the first seeding, 

 a portion of the solution is withdrawn in a sterilized pipette for the pur- 

 pose of determining whether or not the process of nitrification has com- 

 menced ; and if so, to what extent it has proceeded. This may be accom- 

 plished by either determining whether any ammonia has been destroyed 



