76 Mr. E. J. Kussell. 



this we then estimated the percentage absorption of infra-red and ultra-violet 

 rays by such a plate. 



No. of glass. 



Thickness. 



Visual. 



Infra-red. 



Ultra-violet. 





mm. 









256 



2-61 



50 



10-7 



26 -4 



246 



0-86 



50 



18 -6 



20 -4 



217 



1 -55 



50 



6-61 



14-3 



Glass 217 would, therefore, appear to be the most efficient in removing 

 rays likely to injure the eye. Its colour is a pale green, very pleasant to use, 

 and the eye quickly becomes accustomed to the slight coloration. Colour 

 matches appear to be but little affected by it. 



Soil Protozoa and Soil Bacteria. 

 By Edward John Eussell (Rothamsted Experimental Station). 



(Communicated by Dr. Horace T. Brown, F.R.S. Received May 3, 1915.) 



In a paper recently published by Mr. Goodey* it is definitely asserted that 

 ciliates, amoebae and flagellates cannot function as a factor limiting the numbers 

 of bacteria in soils. It does not appear to me that this conclusion is justified 

 by the experimental data given in this paper, and in view of the importance 

 of the subject it seems desirable to bring together the main facts so far 

 ascertained and to summarise the present position of the problem. 



Soil consists of irregular mineral particles of sizes varying from about 

 1 mm. diameter downwards, together with a smaller proportion of organic 

 substances of varying degrees of complexity, nutrient and other salts, and the 

 oxides of. iron, aluminium, and silicon in a form easily soluble in acids or 

 alkalis. The action of the natural processes tends on the whole to effect 

 intermingling of these constituents, at any rate throughout the top 6 inches. 



In its physical properties soil behaves like a colloid ; it possesses strong 

 powers of absorption, and the phenomena are exactly parallel with those 

 shown by other colloids ; it influences the evaporation of water so that the 

 curves become wholly different from those obtained from a water surface 

 or from sand. The evidence all shows that the colloidal constituents are not 

 segregated but are distributed over the surface of the mineral particles. 

 Thus the soil may be looked upon as a mineral framework coated with a 

 * ' Eoy. Soc. Proc.,' B, vol. 88, pp. 437-456. 



