ON THE Economic Coefficient of Slgak 471 



necessity that the irritant substance is acting continually, it is easy 

 to understand that any gain in weight might be indefinitely multi- 

 plied as long as the food supply was sufficient. Since, up to a cer- 

 tain point, the economic coefficient of the sugar rises with the in- 

 crease of dry weight shows that there must be some relation between 

 the two, that the latter phenomenon must in some measure at least 

 be dependent upon the former. The actual gain in the economic 

 coefficient must at any one time be very small and it is highl)- prob- 

 able that given time any two cultures, the one with and the other 

 without an irritant substance added would tend to become equalized. 

 As the weight of the crop falls with the increase of ZnSO., so 

 also does the economic coefficient diminish, but the writer would 

 not be prepared to maintain that the to.xic effect of this substance 

 is in itself merely the diminishing of the economic coefficient to a 

 vanishing point. It is not to be supposed that the irritant salt acts 

 directly on the sugar but on the fungus in which no doubt other 

 and more subtle changes in the "protoplasm are brought about. 

 As was shown indeed in one series even in very much stronger 

 solutions of ZnSO^ w^iere the growth Is materially diminished 

 by the salt, the economic coefficient remains practically the same 

 as in the normal. A further discussion of the toxic action of this 

 salt is, however, not within the limits of this paper. 



While it would be manifestly improper with evidence afforded 

 by only a comparatively i&\N series of experiments from but a 

 single point of view to theorize too widely as to the nature of this 

 chemical irritation, the writer feels justified in arriving at the con- 

 clusion that the increase in the availability of the sugar consumed 

 is at least one factor and an important one in determining the in- 

 crease of growth. In just what way the irritant influences the 

 metabolic activity of the fungus hyphae must be at present at least 

 merely a matter of speculation. The irritant substance is not in 

 itself a source from which energy is available. 



In their action as poisons the salts of zinc, nickel, manganese 

 and lithium would come under the third group of poisons as recog- 

 nized by Locw in his " Xaturliche System der Gift \Virkun<ren," 

 which includes those bases that by their power of forming salts 

 with the protein substances of the protoplasm induce disturbances 



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* Munich, 1893. See also Davenport, Experimental Morphology, i : 12. 



