8i 



IOWA ACADEMY O.? SCIENCES. 



alvei. The causal connection of this germ and "foul blood" was first established 

 by Watson Cheyne.»« 



Many bacterial diseases of insects are beneficial, like "flacherie" of the cab- 

 bage butterfly {Pieris rapae) the bacterial disease of "chinch bugs" {Streptococus 

 insectoruu) carries large numbers of this troublesome pest away. In this country 

 Prof. Forbes'' was the first to study '"flacherie" and other bacterial diseases of insects. 

 That these spread rapidly was shown by Prof. Osborn^' who introduced diseased 

 worms of the cabbage butterfly from Illinois. Later, C. V. Riley. '^ and under 

 him F. W. Mally,'™ carried on some experiments with contagious germs to deter- 

 mine whether the "boll worm" could be held in check. Prof. Snow^^^ of the Uni. 

 versity of Kansas, has also carried on a'long series of experiments with the "chinch 

 bug" disease. From the results obtained by these investigators there is no doubt 

 that if the germs are carried over successfully either by the insects, or cultivated 

 in nutrient media, that they may be utilized with advantage. Of course the insects 

 must be gregarious, so that the disease can be spread easily. It is too soon to make 

 any general predictions concerning the application of this work in holding insects 

 in check, but we may confidently expect that it will find application in applied ento- 

 mology. 



We may note in this connection that Loeflit^r has successfully spread a disease 

 of field mice, Bacillus ti/Dhi-murinum, in Southern Russia, and in this way mate" 

 rially checked this plague. 



BACTERIA OF SOIL. 



Let us briefly turn our attention now to a consideration of the bacteria of soil 

 and the decomposition of organic matter, the formation of nitrates and nitrites. 

 It has well been said that while bacteria cause much misery in the world they are 

 great benefactors. Without them there would hardly be any rot nor decay. 

 Our beautiful landscapes could not exist. The earth, garnished with the bloom 

 of flowers, the green herb, its magnificent forest.*, our cereals and food plants, 

 would not have the material from which to build up their fabric, except for these 

 tiny plants. The nitrogen so essential for all living plants is only made ready for 

 the use of most green plants by these wonderful micro-organisms. 



Nitrification formerly meant the production of niter, a natural product of cer- 

 tain soils and rocks, but modern chemists have given to the word a wider meaning. 

 It concerns the formation of nitrates and nitrites. 



The older theories are discussed in various works on agricultural chemistry^°^. 



The first suggestion that nitrification was caused by a ferment was made by 

 Mueller'"^ but the true nature of nitrification was worked out by the French 



96 Frank R. Chesire and Watson Cheyne, .lournal of the Royal Microscopical Soc. 

 1885, p. 11. 



J. J. MacKenzie, The Foul Brood Bacillus, B. alvei; its vitality and development' 

 18th Annual Report Ontario Agricultural College and Exp. Farm, 1892, pp. 267-273. 



97 Contagious diseases of insects, 111. State Laboratory of Natural History. Bulletin 



98 Iowa Horticultural Report, 1885, Insect Life, Vol. Ill, p. 143. 



99 The Outlook for Applied Entomology, Insect Life, Vol. III., p. 197. 



100 Report on Boll Worm of Cotton, Bull. No. 29, Division of Entomology U. S. Depart- 

 ment of Agriculture, 1893. 



101 Insect Life, Vol. III., p. 279. 



102 Johnson, How crops grow, d. 391, New York, Orange Judd Co., 1888; Storer, 

 Agriculture In its relation to chemistry, etc., etc.; Warrington, six lectures on the 

 investigations at Rothansted Experimental Station, delivered under the provisions of 

 the Lawes Agricultural Trust, before the Ass. Am. Agrl. College and Experiment 

 Stations, Washington, Aug. 12-18, 1891; Experiment Station Bulletin No. 8, office of 

 Experiment Stations U. S. Dept. of Agrl., Washington, Government Printing office. 



103 Land w. Versuchs Stat. Vol. XVI, p. 233. 



