Blackman. — Optima and Limiting Factors . 295 
be arrived at without the disturbing effect of introduced ‘ chemical 
stimuli.’ 
On the conclusion of this survey it will be generally conceded, 
I think, that the way of those who set out to evaluate exactly the effects 
of changes in a single factor upon a multi-conditioned metabolic process is 
hard, and especially so when the process is being pushed towards the upper 
limits of its activity. In this latter department of investigation, I think it 
may be fairly said that at present our science entirely lacks data that will 
stand critical analysis from the point of view indicated in this article. 
Several preliminary analytical investigations in this field are now 
in progress here. 
Cambridge, March , 1905. 
