AC KNO'-XED ai.TEN T 3 . 



The study dealt with in this paper was sug- 

 gested by Dr. B. S. Livingston and carried out un- 

 der his direction. The writer 7;ishes to express 

 his indebtedness to Dr. Livingston for great assis- 

 tance rendered in c^^rrying cut the study and for 

 helpful criticisrn of the manuscript. The writer 

 also wishes to thank Tr. H. E. Pulling for valuable 

 suggestions made during the course of the study. 



