1912.] PUBLIC DOCUMENT — No. 31. 133 



number of Bacillus siibtilis were found in the unsterilized sub- 

 soil decoctions as compared with the sterilized decoctions. 



A careful consideration of our work leads us to believe that 

 protozoa were absent in all our decoctions, and the experiments 

 shown in Table VIII. seem to substantiate this belief ; moreover, 

 protozoa were uncommon in the soils used. A number of sam- 

 ples of the loam and subsoil were subjected to examination, but 

 very few protozoan forms ^ were found. In this vicinity great 

 numbers of protozoa ai'e found in pools of standing water, while 

 few are observed in garden soils. In other localities protozoa 

 may be more abundant in soil; however, no data are available. 

 For protozoa to reduce the bacterial flora of the soil to an appre- 

 ciable degree by devouring the bacteria, it is certain that the 

 number of protozoa present in the soils of Amherst would have to 

 be increased manyfold ; besides, all protozoa do not consume 

 bacteria. G. JST. Calkins, professor of protozoology at Columbia 

 University of New York, is the authority for the following: 

 " All classes of protozoa except Sporozoa are bacteria eaters 

 except the carnivorous forms." The same authority in a recent 

 work - says : " Two of the most striking phenomena among the 

 protozoa arc the apparent choice of food and the selection of cer- 

 tain materials for building shell." The author notes that cer- 

 tain protozoa will live almost exclusively on other protozoa and 

 such vegetable forms as Oscillaria, Spirog}Ta and diatoms. 

 " Each protozoan will eat only its favorite food, although other 

 food is abundant." If the above is true it means that hundreds 

 of protozoan forms of the soil do not feed on bacteria, therefore it 

 is impossible to credit the difi^erence in the numbers of bacteria 

 in a gram of soil ^ — 7,000,000, and a gram of treated soil (ster- 

 ilized) 37,000,000 — to the elimination of the protozoa. This 

 remarkable increase in the number of bacteria of over fivefold 

 of the original number in the untreated soil can only be explained 

 by an increased food supply. In our experiments with soil decoc- 

 tions, where the protozoa were entirely eliminated, we obtained 

 a difl'erence in numbers of bacteria present in the decoctions of 

 sterilized and unsterilized soils ranging from fifteen to twenty 



' The following species were observed: Halteria, Enchelys, Paramoecum, Amoeba, Euglena, 

 Euplotes, Dileptus, Strombidium and Oxytridia. 

 ' The Protozoa, Columbia Biol. Ser., VI., p. 305. 

 ' Hall, Harper's Magazine, October, 1910, p. 681. 



