PREFACE 



The subject-matter of this volume was delivered in 

 the form of public lectures at University College, 

 London, by the several authors, during the first half 

 of 1918. Though the majority of the subjects included 

 appear in the form of more or less acute war prob- 

 lems, there are few of them that do not possess at 

 least as great a value in relation to the enjoyment 

 of peace. Most problems need a crisis before they 

 attract serious attention, and it is just this service 

 which the war has rendered. Our problems are really 

 peace-time problems standing out in relief against the 

 background of the war. 



Thus, so long as population continues to expand 

 indefinitely and the yield of grain is limited' by the 

 area of the earth's surface susceptible to the cultiva- 

 tion of cereals, no one will have the audacity to 

 assert that the determination of the ultimate food and 

 energy resources of the wheat grain is a mere episode 

 of war. 



Then take the beautiful work on the vitamines 

 called forth by the appearance of " deficiency" diseases 

 in several theatres of the war. This is probably little 

 more than the starting-point of an enquiry into these 

 mysterious growth factors, the right understanding of 



