4 
10 Nebraska Experiment Station Research Bui. 15 
bodily comfort. These figures indicate why it is that farmers 
living well within favorable regions give a great deal of 
attention to soil problems, while those in the northern border 
areas are more interested in cold evasive and cold resistant 
crops ; and again in dry border areas interest turns to prob- 
lems of irrigation, drought evasion and drought resistance. 
Of the people living in North America and Eurasia, 90 
to 95 per cent are located within the favorable regions. To lia 
the north scarcity of food and the difficulty of maintaining a ' 
comfortable bodily temperature act as checks to immigra- ?# 
tion. Along low rainfall boundaries the principal check is the 
