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 66 Wisconsin Academy of Sciences, Arts and Letters [Vol. 44 
The results, presented in Table 1, indicate that all biocides used appreciably
decreased the soil micro-population. The most drastic reduction of microorganisms
was caused by calomel and benzene hexachloride. The least harmful effect
was exerted by chiordane. 
 The activity of cellulose- and protein-decomposing microorganisms was appraised
on the basis of a modified method of Richard (1945). The soils were incubated
for two weeks at 24° C in a saturated environment and then transferred
into petri dishes together with the standard cellulose and protein cords.
Cultures with cellulose cords were incubated for one week; cultures with
protein cords were incubated for two weeks. The tensile strength of the cords
was recorded by means of a wire tensilometer, and the results were expressed
in percent of the tensile strength of sterile cords. The averages of quadruplicate
determinations, given in Table 1, indicate that the processes of organic
matter decomposition are retarded to a marked degree by application of all
eradicants. The reaction of cellulose-decomposers and protein-decomposers
suggests that these two groups of microorganisms vary considerably in their
tolerance of different chemical compounds. 
 The rate of nitrification was determined by the standard phenoldisulfonic
method using an Evelyn colorimeter. The samples were enriched in ammonium
sulfate, applied at the rate equivalent to 400 lbs. per acre, and incubated
for 3 weeks at 28° C. The results, reported in Table 1, show a depressing
effect of all eradicants on the activity of nitrifying bacteria, especially
sharply pronounced in treatments with calomel, Stoddard solvent, and chiordane.
 For the determination of the rate of respiration of treated soils, 250 g.
of air-dry samples were placed in 500 ml Erlenmeyer flasks, moistened, and
incubated for 48 hours at 28° C. Before the analyses, 0.5 g. of '
dextrose
was added to each culture. The determination of carbon dioxide evolution
was made by the procedure of Heck (1929), using 48 hour aeration periods.
The results, presented in Table 1, provide a clear-cut picture of the adverse
influence of the biocides. 
 The effect of volatile substances, emitted by soils, was studied using Cholodny's
biotest (Cholodny, 1951; Persidsky and Wilde, 1954). The results of these
trials (Table 1) show that the growth of excised roots of blue lupine is
depressed in part by the direct toxicity of applied chemicals, and in part
by the reduction of the microbiological activity responsible for the release
of growthpromoting volatile substances. As indicated by the average growth
and longevity of roots, calomel and formaldehyde exert