i 5 4 AGE, GROWTH, AND DEATH 



series of modifications of its protoplasm which enable 

 it to accomplish the transmission of the nervous im- 

 pulses with greater efficiency than ordinary protoplasm 

 can do, probably at a higher speed and with a more 

 perfect adjustment of communication between the 

 various parts of the body than is possible with any 

 machinery of pure protoplasm. So, too, the glands 

 have cells which are especially capable of elaborating 

 chemical substances which, when they are poured out, 

 accomplish the work of digestion, for instance. But 

 these cells are likewise alive in all their parts. They 

 have all the fundamental vital properties, but there is 

 a tremendous exaggeration of one faculty, and that 

 involves an alteration so great in the protoplasm that 

 we can see it with the microscope ; the microscope 

 affords us a perfect visible demonstration of differen- 

 tiation, which we can correlate with the function. 



The primary object, therefore, of all differentiation 

 is physiological. The higher organism, with its com- 

 plex physiological relations, is something really higher 

 in structure than the lower organism. The term 

 "higher" in biology implies a much more complex 

 interrelation of the parts, a much more complex re- 

 lation of the organism to the outside world ; and above 

 all it implies in the highest animals a complex intelli- 

 gence of which only a rudimentary prophecy exists in 

 the lowest forms of life, possibly scarcely more than a 

 mere sensation. We owe then to differentiation our 

 faculties, which we prize. It is the result of differ- 

 entiation that I am able, to address you and present 



