468 Richards : The Effect of Chemical Irritation 



Taking the control cultures as a base from which comparison 

 can be made, those cultures to which an irritant substance was 

 added now demanded attention. From the results previously ob- 

 tained such degrees of concentration as showed a marked irritant 

 were employed, the stronger solutions where in the case of the 

 poisonous salts a secondary toxic eflfect was noted, were not em- 

 ployed, except in one series. With this last named exception' all 

 of the ZnS04 series comi-^riscd the following percentages of the 

 anhydrous salt 0.002^; 0.004^; 0.008^; 0.032^; the last 

 named concentration being just within the range of the toxic effect. 

 In those cultures to wliicli iron salts w^cre added, a much greater 

 degree of concentration is indicated, for it will be remembered that 

 iron has a double effect, first as a necessary food substance for the 

 fungus, and secondarily, when present in larger quantities as an 

 irritant. Consequently the percentages of Fe^Cl^. were 0.05 ^0 ; 

 0. 10^; 0.20^. In the same way the lithium salt, in this case 

 lithium chloride, although not an indispensable ash constituent is 

 not effective as an irritant, except in comparatively strong solu- 

 tions, and apparently does not exert any poisonous influence on 

 these hyphomycctous fungi. It was used in the following concen- 

 trations of o. 125 ^ ; 0.350 ^ ; 0.375 ^. ^^ the few scries with 

 nickel salts the sulphate was not used in concentrations' very 

 much greater than with the ZnS04, for like the latter salt it is 

 ultimately a poison. The citations above given are in fractions of 

 a per cent., for the sake of comparison with the writer's previous 

 paper which has already been referred to, but it will be observed 

 that in the tables the equivalents of the solutions are given In frac- 

 tions of the 7/6'/7;/^z/ solution. This method of reckoning In gram- 

 atoms of the irritant or toxic base w^as employed by Kahlenberg 

 and True* and affords a much better standard for comparison for 

 future works in this line than expressions In terms of per cent. 

 Since in every salt used in these experiments herein described the 



I 



acid may be regarded as entirel}' neutral in its effect on the growth 

 of the fungi the whole of the irritant effect is to be referred to the 

 base of the particular salt employed. 



Upon examination of the tables it will be seen that the curve 

 of the economic coefficient of the su^ar rises wuth the increase In 



*15ot. Gaz. 22 : 81-124, 1S96. 



