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 1 11.).^ 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 ^^ (seep. 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. 



330 



