INFORMATION TO SUBSCRIBERS 
SoTBSCRiPTiONS at the rate of $5.00 per annum should be made payable 
to the National Academy of Sciences, and sent to Williams & Wilkins Com- 
pany, Baltimore, or Arthur I/fDay, Home Secretary, National Academy of 
Sciences, Smithsonian Institution, Washington, D. C. Single numbers, $0.50. 
Past publications of the National Academy of Sciences are listed in these 
Proceedings, Volume III, pp. 743-753, December, 1917. In good part these 
pubUcations are no longer available for distribution. Inquiries with regard 
to them should be addressed to the Home Secretary, National Academy of 
Sciences, Smithsonian Institution, Washington, D. C. 
Past volumes of the Proceedings may be obtained at five dollars per volume 
unless the sale of the volume would break a complete set of volumes I to IV, 
Single numbers may be obtained for fifty cents except where the sale of such 
numbers would break up a complete volume. Only two hundred complete 
sets of the Proceedings are available for sale — ^Volumes I to IV, price $20.00. 
Orders should be sent to the Home Secretary, National Academy of Sciences, 
Smithsonian Ins tit tion, Washington, D. C. 
