On Evil in Small Doses 
other salts of zinc, of iron sulphate and lithium chloride 
when Penicillium and other fungi are treated with them.® 
When growing peas and vetches are watered with 
minute doses of copper sulphate such as .00000287 per 
cent. they are distinctly improved and grow more rapidly 
than usual, but a poisonous effect was at once noticed 
even when the solution was only .0000287 per cent.’ 
So also with sodium fluoride and many other poisons. 
When trained by gradual increase of the poison, 
fungi can sometimes be made immune to their effects. 
A yeast has been educated to live in a solution of 
200 gr.per hectolitre of fluoric acid (7.05 ounces in 
22 gallons) which is at once fatal to untrained yeasts 
(see Chapter III.).8 Very small amounts of chloroform 
favour the assimilation of green plants, which are, of 
course, killed at once by larger doses.® Even alcohol, 
when in very dilute solution, accelerates the streaming 
of protoplasm, but the movement is very soon checked 
and may be stopped altogether if the dose is too strong.” 
It is just the same with ether, which has been found 
exceedingly useful in inducing the lilac to flower before 
the usual period, although it is a distinct poison when in 
excess. 
So also as regards electricity and even extremes of 
temperature, it seems to be true that an evil in small 
doses is an excellent stimulus, whereas too much of it is 
fatal (see p. 211). 
Swarm spores, bacteria, and other free swimming plant 
spores are neutral, attracted, or repelled according to 
the amount of heat." A severe frost (— 12° C.) is said 
to improve the vigour of germination in the spores of 
rust-fungi, and also to improve potatoes ” (see p. 293). 
Perennials are said to bloom earlier and to be more 
vigorous in the spring if they have had very cold 
weather ° during the winter rest. 
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