CONTENTS. 
PAGE 
Detection of Induced Beta-Ray Emission from Substances Exposed 
to Rontgen-Rays by a Photographic Method. By Lewis 
Simons, B.Sc.Lond. (With Plate XIV.) . . . * . .297 
Experimental Infestation of Fresh- Water Snails. By E. G. Cawston. 301 
Some Notes on Ancient Ideas concerning the Diamond. By J. R. 
Sutton 305 
A Study of the B. coli Group with Special Reference to the Sero- 
logical Characters of these Organisms. By T. J. Mackie . . 315 
A Contribution to the Study of the Rainfall Map of South Africa. 
By J. R. Sutton. (With 13 Maps.) 367 
