THERMOGRAPHS OF REGIONAL DEATH 1 85 



bath, the fatigued style underwent the change from white to 

 brown at 56 C, whereas the test specimen was not discoloured 

 until 64° C. 



Determination by thermographic method of relative 

 excitatory effects of anode and kathode. — This thermo- 

 graphic method also enables us to attempt the solution of 

 other recondite problems, such as that of the relative excita- 

 tory effects of the anode and kathode. It will be shown in 

 the next chapter that when the electromotive force is not too 

 excessive, it is the kathode which causes excitation when the 

 circuit is made or completed. This fact will be demonstrated 

 there by experiments undertaken with sensitive plants, in 

 which the excitatory effect is indicated by the mechanical 

 response of the motile leaflets. No such means is available, 

 however, in the case of ordinary, or so-called non-sensi- 

 tive, tissues. In such cases, therefore, I shall undertake 

 to demonstrate the same fact, but by means of death- 

 response. 



We have seen that a tissue which has already been 

 excited, is more fatigued than one which has not, and a 

 fatigued tissue is, as we have seen, subject to death, and 

 subsequent discoloration, at lower temperatures than the 

 unfatigued. Hence, if excitation be caused in the kathodic 

 region at make, death-discoloration ought to occur there 

 earlier than in the anodic. This I have been able to 

 demonstrate in the following manner : I took two similar 

 petals, or two halves of the same petal, of Passiflora. The 

 two were held side by side in a glass vessel full of water, 

 at a distance of 3 cm. from each other, the temperature 

 being gradually raised. When the temperature is about 

 50 C. a current is sent from a battery so that it enters 

 by one petal, and leaves by the other. It is now found 

 that the discoloration of death takes place earlier at the 

 kathode than at the anode. The value of the difference is 

 about 4 C. I carried out this experiment on the petals of 

 the crimson Sesbania coccineum also. 



