86 THE SIGNS OF LIFE [LECT. 



synthesis and accumulation. The vegetable, in most immediate 

 contact with inert things, combines, organises, and accumulates. 

 The animal, in less immediate contact with inert matter, disrupts, 

 utilises, and dissipates in their fragments organic compounds 

 that it has received ready-made from other animals and from 

 plants. And quite early in its development the external surface 

 of the animal is distinguishable into two parts: (i) a surface 

 principally receptive of incoming matter, the digestive and 

 absorbent surface ; (2) a principally emissive surface, the ex- 

 ternal skin, through which the greater moiety of animal energy 

 is dissipated. An " organ-current of action," if aroused in these 

 surfaces, should, according to their several physiological habits 

 and dispositions, be : 



Principally ingoing for the vegetable " skin." 

 Principally outgoing for the animal skin. 

 Principally ingoing for the animal mucosa. 



52. Some experiments. And whatever the fate of our 

 theoretical motive, it will have served to instigate a search for 

 facts ; but we must take due care to emancipate observation 

 from expectation, and not merely see that which we expect 

 or hope to see. Here is a piece of orange peel, chosen for our 

 purpose not merely because it is a handy object, but because the 

 " skin," presumably living, is easily separated from the " body " 

 of the fruit by breaking through "subcutaneous tissue," pre- 

 sumably not-living. And in point of fact, you notice that the 

 bit of orange peel, placed between unpolarisable electrodes, 

 exhibits little or no current, unlike a paring of an apple or a 

 potato that necessarily has an injured inner surface, and ex- 

 hibits, therefore, a strong outgoing current of injury. I com- 

 pensate precisely and then test in the way now familiar to you 

 (plug the galvanometer, send an induction shock through skin, 

 unplug the galvanometer), and you see that to both + and 

 directions of excitation the orange peel responds by a deflection 

 to your left, signifying current of negative or ingoing direction, 



53. Human skin. - -I next take a piece of human skin, 

 twenty-four hours after excision, and test it in the same way 



