118 M('tho(h /(»' Examination of Soil Priito-jia 



groups on the decaying organic matter in the soil, possibly onl_\' for 

 short periods, and that the encysted forms present in the soil are favoured 

 by the condition of the culture at the expense of the smaller flagellate 

 forms, or it is possible that these large flagellates are contented with 

 a very short trophic life in the soil at a time when the water content 

 is high and there are large quantities of decaying material in the soil. 



Under these conditions it is not unlikely that the ciliates so frequently 

 found in soil cultures lead a trophic life in the soil. 



There is another factor which must be reckoned with in this con- 

 nection, and that is the possibility that the present methods for the 

 examination of fresh soil films do not give a fair account in regard to 

 these large flagellates, which may be caught up by their flagella amongst 

 the soil particles. 



None of these possibilities is mutually exclusive, and it seems from 

 recent work on cultures of soil to which water alone has been added 

 that the last explanation is not very probable. 



In conclusion, it seems to us that there are three categories under 

 which the protozoan population of any soil at a given moment should 

 be studied, (1) the active fauna, (2) the resting fauna (in cysts), and 

 (3) the cultural fauna. In the immediate future better methods must 

 be devised for the detection of the active fauna, a complete study is 

 needed of the possible seasonal variations which might result in a 

 transfer of certain forms from the resting fauna to the active fauna, 

 and a more careful study must be made of cidtural conditions, so that 

 it may be jDossible to cultivate at once any desired member of the 

 active fauna of a soil. 



LITERATURE LIST. 



1. BuTSCHLl. "Protozoa" in Bronn's Tierreich, 1880. 



2. ClENKOW.sKl. Arch. f. mihr. Anal. 187G, 12, 15. 



3. Cunningham aiul Lohnis. Cenlr. liakt. Par. Abt. ir. l!li:i. 39. ")9(>. 



4. Cunningham. J. Agr. ScL, This vol., p. 49. 



5. Ehrenberg. Die Infusorien als voUkommene Organismen, 1837. 



6. GooDEY. Proc. Roy. Soc. 1911, 84 B, 105; Arch. f. Prnl. 1914, 35. So. 



7. Greef. Arch. f. mihr. Anal. 1806, 2, 299. 



8. Leidy. U.S.A. Geological Sxrrei/. ]8(i9. Vol. 12. 



9. >Urtin. Proc. Hoy. Soc. 1912. 85 B, lOr.. 



10. Martin and Lewin. Phil. Trans. 1914, 205 B, 77. 



11. Rahn. Cenfr. Bakl. Par. Abt. ii. 1913, 36, 419. 



