332 



EFFECT OF CHEMICAL AGENTS 



[Cn. XI 



ments and heightened metabolism. To the cases previously 

 given may be added the experiments of SCHULZ ('88), who 

 found that various poisons, such as corrosive sublimate, iodine, 

 bromine, and arsenious acid, increase the activities of yeast in 

 fermentation. It is not strange, therefore, to find that poisons 

 ma} r , at a certain concentration, accelerate growth. That they 

 do so follows from the experiments of RICHARDS ('97), who 

 reared the molds Aspergillus, Penicillium, and Botrytis in 

 nutritive solutions to which had been added small quantities 

 of zinc sulphate, other metallic salts, cocaine, morphine, and 

 other alkaloids. After five to seven days Aspergillus, reared in 

 nutritive solutions in which sugar was the organic compound, 

 had gained the following dry weights (in milligrammes). 

 In all the experiments, except those in the column headed 

 " Control," the solution contained certain non-nutritious sub- 

 stances in from 0.002% to 0.033% concentration. 



TABLE XXXV 



SHOWING THE TOTAL DRY WEIGHT IN MILLIGRAMMES OF A CROP OF ASPER- 

 GILLUS REARED IN THE ABSENCE AND IN THE PRESENCE OF VARYING 



QUANTITIES OF IRRITATING SUBSTANCES 



It is clear from this table that the addition of even small quan- 

 tities of innutritions and poisonous substances may so excite 

 the hylogenic processes as to cause twice or even far more than 

 twice the normal formation of dry substance in a given time, 

 and that this excessive growth increases with the concentration 

 of the salt up to a certain optimum, beyond which growth 

 declines again to below the normal. Similarly TOWNSEND 

 ('97) has observed that a seedling living under a bell jar 

 whose atmosphere contains a small quantity of ether grows 



