470 Richards: The Effect of Chemical Irritation 



ratio over that found in the control cultures corresponding to that 

 found in other experiments. A few series were tried witli a nickel ' 

 saltj the results falling in line with those obtained with the ZnSO^ 

 cultures, the cuive of the economic coefficient of the sugar follow- 

 ing a course similar to that of the gain in w^eight. ^ 



In order to compare the abnormal growth caused by these in- 

 organic salts with that produced by organic substances a couple of 

 series were carried through with cocaine as an irritant. As is 

 shown in the previous paper these fungi do not respond very v^io- 

 lently to the organic substances therein mentioned and cocaine was 

 selected as being the most potent. The results were surprisingly 

 definite ; as will be seen a distinct increase of weight resulted with 

 also an appreciable gain in the ratio amounting to about 0.04. 



It will be seen that, although the effectiveness of sugar as a 

 source of organic nutrition increases in general with the increase 

 of growth induced by the irritant substance and diminishes as the 

 latter diminishes, the economic coefficient does not exactly parallel 

 in Its curve the gain of dry substance. For instance, supposing 

 that the dry weight of a control culture be i and the economic 

 coefficient of the sugar be 0.50, although the dry weight of a cul- 

 ture under similar conditions but with the addition of an irritant 

 be 2 the economic coefficient is not i.oo but much lower on the 

 average, say 0.60. Indeed, it is not to be expected that the eco- 

 nomic coefficient should vary In the same proportion as the Increase 

 of weight. Such an example as given above — the ratio of weights 

 Is often higher as much as i to 3 — would require that all of the 

 sugar used be available for the production of the fungus mycelium, 

 an impossibility in any ev^ent since such a condition would preclude 



d ■ 



the respiration of any CO^. Nor Is it necessary that the available 



r 



portion of the sugar used increase In a similar proportion to the 

 dry substance, for it will be remembered that the effect of the irri- 

 tant substance must, as long as the food supply Is not greatly ex- 

 hausted, be cumulative. Iwen a smaller increase of the economic 

 coefficient of the sugar than that absolutely found would serve to 

 account for a considerable Increase in weight. It is evident from 

 the experiments that of the sugar used more Is actually available 

 for the fungus and that provides for and implies a more rapid growth 

 of tlie latter. Granting this together with the accompan}'Ing 



