1916] CHILD—GRADIENTS IN ALGAE 95 
limits and with certain precautions can be used very widely as a 
means of comparing the general metabolic condition of different 
individuals, and of different regions of the body of a single indi- 
vidual. The method is so simple as to appear crude, but its deli- 
cacy and value have been shown very clearly. Practically it 
consists simply in finding the survival times of the different indi- 
viduals or body regions to be compared in a concentration, deter- 
mined by preliminary experiment, of the agents employed. I have 
found the cyanides particularly satisfactory for animals, because 
they are effective in very low concentrations and for various other 
reasons, but many other substances and conditions can be used in 
the same way. 
In the two modifications of the method we have two ways of 
testing susceptibility and so of comparing general metabolic activity 
or fundamental features of it in different individuals and body 
regions. The first, in which susceptibility is directly determined by 
means of lethal concentrations, I have called the direct suscepti- 
bility method; the second, in which it is determined indirectly 
through the capacity for acclimation, I have called the indirect or 
acclimation method. The direct method is simpler and more satis- 
factory for most purposes, but can be controlled in many cases by 
the indirect. 
By means of these methods, checked and controlled by others, 
I have been able to demonstrate the existence of axial metabolic 
gradients as a characteristic feature of the animal organism, and 
various other lines of experiment indicate very clearly that the 
physiological axes are fundamentally metabolic gradients. 
In my attempt to determine whether such axial gradients are 
_ present in plants the direct method was used, with the following 
procedure. The living plants, freshly collected, were first stained 
with the vital stain, neutral red, and then were placed in a solution 
of potassium cyanide in sea water. The neutral red was used as 
an indicator to make possible the determination of the time of 
death with some degree of exactness. In the plants thus stained 
and then killed in cyanide or various other agents of the proper 
3 These methods and some of their results have been considered in the following 
publications: Cumip, C. M., 4-10, 11 (particularly chapter iii), 12. 
