822 EXPERIMENT STATION EE(,'ORI). [Vol. 41 



sterilization appears to be due largely in some cases to lateness or slowness 

 in germination, though occasionally the production of new spores seems to be 

 influential in this respect. The surest means to exterminate bacteria with 

 temperatures not exceeding 100° C. is to subject the medium several times to 

 high tempei-atures on successive days, with room temperature during the in- 

 tervals. High degrees of resistance possessed by spores are due predominantly 

 to impermeability of their membranes. 



After repeated infection in liquid media (during two to five months) the 

 spores lost the power of resistance due, apparently, to the increase of permea- 

 bility of their membranes and their resulting too great readiness to germinate. 

 After drying on soil, sand, or kaolin for a few weeks resistance may reappear 

 in such spores. The species studied were aerobic, germinability being rapidly 

 decreased by lowering the oxygen pressure and increased by restoratii^n of the 

 normal oxygen supply. 



Studies on the proteolytic enzyms of soil fungi and Actinomycetes, S. A. 

 Waksman {Jour. Bad., 3 (1918), No. 6, pp. .50.9-530).— Employing in tlie present 

 investigation methods of isolation and description of soils identical with those 

 used in a former contribution (E. S. R., 36, p. 214), the author has made a 

 study of a number of organisms isolated from different soils, chiefly of Asper- 

 gillvs niger. 



It is stated that the proteolytic enzyms contained in the fungi studied ap- 

 pear to differ from known proteolytic enzyms of animal oi'igin inasmuch as 

 they have a greater range of optimum reaction and a lower temperature 

 optimum. They are not precipitated by safranin. The exoenzyms can pass 

 through a Pasteur-Chamberland filter. Their production of proteolytic exo- 

 and endoenzymos (as regards A. niger) is not affected by the sugar content 

 of the medium. Both exo- and endoenzyms are produced by microorganisms 

 on protein-containing and protein-free media. The age of the culture at which 

 the most active enzyms are obtained depends on the organism itself, its rapidity 

 of growth, and the nature of its waste products. Fibrin and crystalline egg- 

 albumen are decomposed by both the exo- and endoenzyms. The fact that 

 small quantities of ammonia are produced in the decomposition of peptone 

 and casein by the proteolytic enzyms of the microorganism suggests the 

 presence of desamidases among the enzyms produced. 



FIELD CROPS. 



Crop rotation and soil fertility, R. C. Doneghue {North Dnkota Sta. Bui. 

 126 {1918), pp. 197-251, flgs. 13).— The first part of this bulletin (pp. 197- 

 216) deals with a study of cropping systems for the Red River Valley of 

 North Dakota made during the 7-year period of 1910-1916, in an effort to de- 

 termine the income that could be obtained when crops were placed in a rota- 

 tion where the value of each crop could be fully realized. Various five and six 

 year rotations have been followed, while observations have also been made 

 on plats grown continuously to brome grass for 11 years, to wheat for 34 years, 

 and to alfalfa for 5 years. The effect of manure on the various crops is also 

 noted. The yields and estimated values of the crops are presented in tabular 

 form and the results secured summarized as follows: 



Tlie black clay soil of the Red River Valley has deteriorated in fertility and 

 crop producing capacity under a system of continuous cropping with wheat. 

 Such land on the station farm contains approximately one-fourth to one-third 

 less nitrogen and one-fifth less phosphorus than virgin soil of the same type. 

 The yield during the last eight years has been 28 per cent less than during the 

 fir.st eight years of a 24-year period. A total application of 135 tons of 



