310 DR. T. C!001)EV OX 



of their life-histoi'ies ; also whether they are forms capable of 

 consuming bacteria, and thus able to function as a limiting factor 

 on soil- bacteria. 



One of the chief methods by which soil-protozoa can be 

 studied is examination in cultures made in suitable media ; and 

 although it has recently been claimed * that tlie cultural forms 

 are not necessarily those occurring in a trophic condition in 

 the soil, and may not therefore be concerned iji the biological 

 changes of the soil, yet I have quite recently obtained some experi- 

 mental i^esults which point most positively to the cultural protozoa, 

 especially amo?bfe, acting as a check to the increase of bacterial 

 numbei'S. I hope to publish an account of this work shoitly. In 

 the present paper an account is given of a few forms of flagellates 

 and amoeba? which were obtained culturally from some old soils 

 stored at Kothamsted Experiment;il Station, together with some 

 observations on their cytology and methods of division. The 

 protozoan fauna of these soils was a limited one when compared 

 with that of an ordinary garden or iield-soil, and for this leason 

 presented a suitable field for working out the difteient organisms 

 in detail. 



In a recent number of ' The Annals of Applied Biology ' I have 

 recorded the culture of amceb* and flagellates from soil bottled 

 so far back as 1865 and left untouched since then ; thus proving 

 the survival of protozoa, no doubt in an encysted condition, for a 

 period of 49 years. It was my intention at the outset of the work 

 merely to obtain an idea of the character of the protozoan fauna 

 surviving in the different soils examined. In order to do this, 

 and to determine as nearly as possible the different species which 

 cropped up, it Avas necessary to make a number of permanent 

 stained preparations and to study these in considerable detail. 

 As a result of these observations, I have obtained a number of 

 interesting facts on the cytology, mode of nuclear division, etc., in 

 several of the forms examined. 



The samples of soil tested for protozoa were taken from bottles 

 of soil obtained originally from five of the fields under experi- 

 mental cultivation at Rothamsted. These were : Bi'oadbalk soil 

 bottled in 1865, Geescroft soil bottled in 1865, Agdell soil bottled 

 in 1867, Hoosfield soil bottled in 1868, and Barntield soil bottled 

 in 1870. 



Methods. 



As a culture medium, saline egg-albumen was used and found 

 very serviceable. A small quantity of soil was placed in this 

 medium, contained in a circular flat-bottomed glass dish furnished 

 Avith a close-fitting flat lid. This Avas then put into an incubator 

 at 22° C, or left at room-temperature. After a fcAv days, micro- 

 scopic examination of the culture revealed actiA^e protozoa. These 

 Avere frequently found on the surface or at the bottom of the 



* Russell, E. J., " Soil Protozoa and Soil Bacteria." Proc. Ko}-. Soc. B, vol. Ixxxix. 

 p. 76 (191-5). 



