61 



Seven new species of flagellates are described, of which, 

 however, five have subsequently been found in soils from non- 

 arctic regions. 



XLI. H. Sandon and D. W. Cutler. "Some Protozoa 

 from the Soils Collected by the ' Quest ' Expedition." 

 Journal of the Linnean Society (Zool.), 1924. Vol. 

 XXXVI., pp. 1-12. 



Soils were examined from St. Paul's Rocks, South Georgia, 

 Elephant Island, Tristan da Cunha, Gough Island, St. Helena, St. 

 Vincent, and San Miguel Azores. The protozoa found in the 

 soils of these remote lands are mostly identical with those found 

 in almost any ordinary English soil. It appears that there is a 

 fairly well defined and characteristic soil protozoan fauna, which 

 is practically ubiquitous. The richest fauna were those found in 

 soils from Tristan da Cunha and Gough Islands, which had been 

 manured with the dung of farm animals for many years. The 

 poorest samples were from South Georgia and St. Vincent, which 

 were all practically sub-soils. 



XLII. D. W. Cutler. " The Action of Protozoa on 

 Bacteria when Inoculated into Sterile Soil.' > Annals 

 of Applied Biology, 1923. Vol. X., pp. 137-141. 



Three portions of sterile soil were inoculated with bacteria 

 alone, bacteria and amoebae, bacteria and flagellates. The 

 bacterial numbers were counted daily. The experiment showed 

 that the bacterial population in soil free from protozoa is able 

 to maintain a higher level for a longer period than when protozoa 

 are present; and that the presence of protozoa is one of the 

 factors concerned in keeping the numbers of bacteria below the 

 level they might otherwise attain. 



XLIII. R. V. Allison. " The Density of Unicellular Orga- 

 nisms/' Annals of Applied Biology, 1924. Vol. XI., 

 pp. 153-168. 



The density of certain unicellular organisms of known 

 diameter has been measured by Stokes' formula. 



The average density of algal cells studied is 1.098 and that 

 for the cysts of Gonostomum sp. 1.057. 



The density of the algal cells was found to vary greatly 

 between the larger and smaller sizes, while for intermediate cells 

 it is fairly constant. The total variation in average density of 

 protozoan cysts was much less marked. 



During maturation, the cysts of a certain species of Colpoda 

 decreased to one-fourth their original volume, while their average 

 density increased from 1.04 to 1.06. 



By the application of the formula of Hehner and Richmond 

 to the density values so obtained, a tentative value has been 

 derived for the actual dry matter of the cells studied. On this 

 basis the dry matter of the young cysts (4 day) of Colpoda sp. 

 amounts to 10.6 per cent, while at the later stage (20 day) it is 

 15.1 per cent. 



