PREFACE 



IX 



burden of these lectures they are deeply indebted to their 

 colleagues both for. able and willing assistance in the 

 presentation of the lectures and for helpful suggestions 

 in the preparation of the text. Where so many have been 

 of great assistance it is practically impossible to make 

 acknowledgment of each separate favor. The general 

 nature, however, of our obligations will be indicated by 

 the following. President Wilbur has regularly given 

 three lectures on disease in animals and one on the rela- 

 tion of human progress to scientific discovery. Professor 

 Doane has given generously of his time and advice in 

 connection with the lecture on insects and disease, and 

 Professor McMurphy has been similarly helpful with 

 plant diseases. Dr. Alsberg of the Food Research Insti- 

 tute has been helpful in our discussion of the structure 

 and functions of protoplasm. Professor Walter Fisher, 

 of the Hopkins Marine Station, has regularly presented 

 the subject of distribution of land animals, as well as 

 having been of service in the general organization of the 

 course. Professor Abrams has regularly given the lecture 

 on geographic distribution of plants and has likewise 

 been of service in the discussion of many other matters. 

 The contributions of Dr. Vestal, director of the labora- 

 tory, have been so numerous and varied as to defy speci- 

 fication, but their value is evidenced by the frequent use 

 made of them. They range all the way from the de- 

 livery of lectures on ecological distribution of organisms 

 to the selection of suitable illustrations. Dr. Becking, 

 who will henceforth be associated with Dr. Vestal in the 

 direction of the laboratories, has also already made many 

 stimulating suggestions, many of which have been of im- 

 mediate use in writing this text. Professor J. P. Smith 

 has assisted in various ways in connection with geological 

 distribution of organisms. We are also indebted to 

 various authors and publishers for permission to repro- 

 duce figures from their books or for original photographs. 

 Specific acknowledgment is made of each such favor in 



