218 Bacteriological Department. [Bull. 161 



which had been plowed under the year previous and had not 

 entirely decayed. The piece of manure, to all appearances, 

 had been pressed into some rodent's runway by the horses' 

 hoofs. The average depth of the previous plowing was ap- 

 proximately four inches. The same thing occurred in the 

 samples taken on the same day on plot 4A. The number of 

 bacteria reached forty-two million per cubic centimeter in the 

 fourth inch and thirty-nine million per cubic centimeter in the 

 sixth inch. Again, on April 9, plot 3A showed sixty-one mil- 

 lion per cubic centimeter in the sixth. This was also due to 

 manure. Another factor which probably induced these large 

 numbers was the increased temperature, followed by a warm 

 two-inch rain which fell about twenty-four hours before the 

 samples were taken. This view is strengthened by glanc- 

 ing through the twelve tables and comparing estimates for 

 April 23. The sandy soils, which allowed a rapid percolation 

 of water, showed a marked increase in number of bacteria, 

 even in the tenth and twelfth inches, but the more tenacious 

 silt soils showed a decrease in the number of bacteria. The 

 temperature of the silt during the preceding week was 15 de- 

 grees C., while on April 23 it had fallen to 14.9 degrees C. 

 The temperature of the sand was 14.9 degrees on April 16, 

 while on April 23 it had risen to 17 degrees C. Plot 4B shows 

 an unaccountable high number in the twelfth inch on the 16th 

 of April. 



The tables show that the number of bacteria increased and 

 diminished with more or less regularity. It was also observed 

 on the plate cultures that one species of bacteria would pre- 

 dominate, and at times almost entirely exclude other species. 

 For instance, on April 9 the sixty-one million count consisted 

 almost entirely of minute oval colonies, all of which were ap- 

 parently of one species. 



On May 13 both plots A and B gave results that were ex- 

 ceptional. On the plate cultures there were innumerable tiny 

 colonies so closely set that they could not be accurately esti- 

 mated. However, estimates placed them at one hundred mil- 

 lion per cubic centimeter. One week later, May 20, all the 

 plots showed a marked decrease in the number of organisms. 

 This was perhaps due to the excessive moisture, the ground 

 having been completely saturated for several days; neverthe- 



