6 BULLETIN 118. U. S. DEPARTMENT OF AGRICULTURE. 



are readily shaken out, it can not be mixed as thoroughly as desired, 

 and consequently there is no way under ordinary field conditions by 

 which a small sample may be obtained that will be truly repre- 

 sentative. 



The errors due to sampling are necessarily large, and the differ- 

 ences in the results from the controls show the extent of this varia- 

 tion. This is unavoidable and must be recognized in all work on 

 manure, and applies to the bacteriological results as well as to the 

 chemical data, but is not so pronounced in the former cases, as the 

 difference between the counts of the controls and treated samples is 

 so much greater than for the chemical results. 



In order to secure the most uniform samples under these conditions 

 for bacteriological and chemical analyses, the following procedure 

 for obtaining samples was adopted. Approximately an inch of mate- 

 rial was first removed from the top and then half a pound of the 

 underlying manure weighed on a spring balance ; another half pound 

 was then weighed from the center of the pile, and finally the same 

 quantity was taken from the bottom. The three samples were all put 

 in the same container for transportation to the laboratory, where the 

 whole sample was spread out on a clean sheet of wrapping paper and 

 then cut into small pieces and thoroughly mixed. When the material 

 appeared quite uniform the sample was quartered. One quarter was 

 then cut into half-centimeter lengths with clean shears. The straw or 

 shavings were cut with the other material. TVhen this was completed 

 the sample was again thoroughly mixed. As the bacterial content 

 of manure is very high, no attempt was made to work under abso- 

 lutely sterile conditions because the contamination arising from ordi- 

 nary handling of the material was of no importance when compared 

 with the great number of organisms present. However, precautions 

 were taken to prevent excessive contamination by using clean paper, 

 shears, etc., for each sample. The carefully prepared quarter sample 

 was put in a clean Mason jar. 



BACTERIOLOGICAL EXAMINATION. 



Two 10-gram samples of the manure, prepared as described above, 

 were taken for each bacteriological determination. A sterile spatula 

 was used to convey the sample from the jar to the tared watch glass 

 on the balance pan. One of the 10-gram samples was dried at 100° C. 

 for one hour to determine the percentage of solids. The other sample 

 was brushed into a 2-liter flask containing 1 liter of sterile water. 

 The cotton plug was thereupon replaced by a clean rubber stopper 

 which had been lightly flamed. The flask was then vigorously shaken 

 for five minutes and again, after a five-minute interval, for three 

 minutes. A 1 c. c. sample was then withdrawn and run into 100 c. c. 



