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HERMANN AUGUST HAGEN. 421 



tific bibliographies. The titles are arranged alphabetically under the 

 names of the authors, and under each author's name in chronological 

 sequence ; entries are made under initials and pseudonyms when these 

 alone are known, and anonymous works are arranged by subjects. An 

 excellent and very detailed synoptic register affords easy reference, and 

 adds greatly to the usefulness of the work. Like all his work, this 

 was prepared with the most laborious painstaking; the libraries of 

 Germany, France, Belgium, Holland, and England were examined, 

 and an amount of drudgery that would have discouraged many was 

 overcome by hard and persevering work. 



From the study of various papers written by Dr. Th. Bail, Dr. 

 Hagen became convinced that the ravages of various injurious insects 

 could be readily cheeked by the application of the yeast fungus, and 

 his paper on the " Destruction of Obnoxious Insects, Phylloxera, 

 Potato Beetle, Cotton Worm, Colorado Grasshopper, and Greenhouse 

 Pests, by the Application of the Yeast Fungus," (Cambridge, 1879,) 

 though based on the mistaken assumption that the beer yeast fungus 

 (Sacc/iarontyces cerevisice) enters an insect's body and produces a dis- 

 ease, caused much discussion. Metschnikoff was thus led to examine 

 several minute parasitic fungi, and was able to prove experimentally 

 the deadly character of " green muscardine " (Isaria destructor) to 

 insects exposed to infection. In his efforts to cultivate the " green 

 muscardine" apart from the insects themselves, Metschnikoff used 

 beer-mash successfully, producing thus a poison which once set ar work 

 multiplied and spread spontaneously, and it is probable that we have 

 here the true explanation of the value of the application of yeast to 

 plants affected by insects. 



In 18G7 Dr. Hagen left Konigsberg and accepted the invitation of 

 Professor Louis Agassiz to take charge of the entomological department 

 of the Museum of Comparative Zoology at Cambridge ; in 1870 as Pro- 

 fessor of Entomology in Harvard College he commenced his Univer- 

 sity career. Dr. Hagen entered upon his duties at the Museum with 

 great zeal ; and his detailed plan for the arrangement of the collec- 

 tions, though somewhat modified, is, and is likely to remain, the basis 

 for the future. Deeply interested ia everything relating to museum 

 work, as his appreciation of series of specimens, his care for their 

 preservation and for the accuracy of their localities, and many minor 

 details, clearly indicate, it is in this collection as well as in his writings 

 that his contributions to science are to be found. Here alone we can 

 fully realize the extent of his discoveries, the keenness of his insight, 

 his skill at preparation and dissection and with the pencil. I lis devo- 



