A Note on the Protozoa from Sick Soils. 



393 



with the diet. It is interesting to note, however, that this tissue has a 

 higher cholesterol-content than any we have examined, with the exception 

 of brain. In six animals the average total free and combined cholesterol 

 is 0*5022 per cent., the free cholesterol - 4493 per cent., and ester 

 cholesterol 0'0529. The ester cholesterol was very variable and, in two 

 cases, nil. 



We take this opportunity of expressing our thanks to the Government 

 Grant Committee of the Koyal Society for assistance in carrying out this 

 work. 



A Note on the Protozoa from Sick Soils, with some Account of 



the Life-Cycle of a Flagellate Monad. 

 By C. H. Martin, M.A., late Demonstrator in Zoology at Glasgow University 

 and at the Imperial College of Science. 



(Communicated by Prof. E. A. Minchin, F.E.S. Eeceived May 10, — 

 Eead June 20, 1912.) 



[Plate 10.] 



Of recent years a great deal of attention has been attracted to the subject 

 of sick soils, i.e. soils of which the produce has fallen off without the decrease 

 being definitely attributable to the lack of plant-food in the soil. In this 

 preliminary note I should like to deal shortly with some aspects of this 

 question from a zoological point of view, and also to describe the life-cycle of 

 a flagellate monad which happened to be one of the organisms from this 

 source, of which I have succeeded in obtaining pure animal cultures. I hope 

 to describe cultures of this and other forms in greater detail in a forthcoming 

 paper. 



The literature on this subject from a botanical and chemical standpoint 

 will be found in a paper by Dr. Eussel and Dr. Hutchison "On the Effect 

 of Partial Sterilisation of Soil on the Production of Plant-Food,"* and it is 

 particularly to this work that we owe the insistence on a hypothesis which 

 is full of interest to the zoologist, namely, that the activity of protozoa in 

 these soils may in many cases be a factor in bringing about soil-sickness. 



It is obvious that one of the first steps in the discussion of this problem 

 must be the elucidation of the normal protozoan population of a soil. 



* 'Journal of Agricultural Science,' 1909, vol. 3, Part II. 



