DESTRUCTION OF FLY LARViE IN HORSE MANURE. 7 



of sterile water. Five dilutions were prepared, ranging from 1 part 

 in 10,000 to 1 part in 100,000,000. A duplicate series of Petri dishes 

 was then prepared from these dilutions and standard beef agar. 

 After five days' incubation at 28-30° C. the plates were counted. The 

 average counts of the duplicate plates were taken and converted into 

 equivalents for 1 gram of dry manure by the use of the figures ob- 

 tained from the duplicate 10-gram samples that had been dried at 

 100° C. 



The results obtained by plating on the standard beef agar are com- 

 parative and serve to show the germicidal action of the chemicals on 

 the majority of the bacteria present in the manure. The total bac- 

 terial counts on this medium include not only some of the bacteria 

 that increase the value of the manure by their metabolic processes, 

 but also many that may decrease its value in the same way by de- 

 stroying nitrogen salts available for plant food. For this reason the 

 total bacteriological counts on beef agar are not considered as entirely 

 indicative of the fertilizing value of the manure. Ifc is even possible 

 that the germicidal effect of formaldehyde, calcium cyanamid, and 

 potassium cyanid in the manure might prove highly beneficial, as 

 Russell and Buddin's (1913) results with formaldehyde, toluene, 

 cresol, phenol, etc., in the soil indicate. 



CHEMICAL EXAMINATION. 



The method of taking the samples was described above, but the 

 samples for chemical examination were twice run through a sausage 

 grinder after cutting with shears and were placed in screw-capped 

 Mason jars provided with rubbers and analyzed as soon as possible. 

 Samples for chemical examination were taken from the control cages 

 immediately after the experiments were started, and from all 15 

 cages after 10 days. In this way it was thought an idea of the 

 change which had taken place in the various samples could be ob- 

 tained, the changes in the controls being taken as an index of the 

 normal rate of decomposition of the manure. 



The manure samples were analyzed for solids, ash, ammonia, and 

 nitrogen, using the methods of the Association of Agricultural 

 Chemists (Wiley, 1908). The total nitrogen determinations were 

 made by the nitrogen laboratory of the Bureau of Chemistry. The 

 results obtained by the magnesium oxid distillation method for am- 

 monia, although much higher, showed the same general tendencies 

 as the results obtained on the water extracts. 



Water extracts of the manure were prepared from each sample 

 by taking 25 grams of the finely divided manure and adding 500 c. c. 

 of distilled water, allowing them to stand for one hour, with occa- 

 sional shaking. The solutions were filtered through S. & S. folded 

 filters No. 588, and the following determinations were made : Water- . 



