622 THE WONDER OF LIFE 



One of Harrison's devices was to excise a small portion 

 of nerve cord from an embryo frog, and to replace this by a 

 cylindrical clot of blood or lymph of the proper length and 

 calibre. After two or three days the embryo was killed 

 and sectioned. It was found that fibres from the brain 

 and anterior part of the cord had grown, or flowed, for a 

 considerable distance into the cord, forming naked threads. 

 But the general point with which we are here concerned 

 is that the development of nerve-fibres is brought about 

 by one of the very primitive properties of protoplasm, 

 namely amoeboid movement. 



It is very interesting that the only animal types 

 without wandering phagocytes are the Nematodes 

 (some of which at least have stationary phagocytes) and 

 the Lancelets. The Nematode worms do not lead on 

 to anything else ; and the Lancelets, though near the 

 base of the Vertebrate branch, are specialized types 

 on a cul-de-sac of their own ! It appears to us profoundly 

 significant that Man himself in the development of his 

 nervous system, in the repair of an injury to the front of 

 his eye, in the everyday resistance to intruding Bacteria, 

 and in every inflammation, serious or trivial, harks back 

 in his cellular activities to the Amoebae gliding along on the 

 mud of the pond. 



VITALISM 



The Purely Physical. Among the facts with which the 

 student of science has to deal there are many which he 

 calls purely physical the movements of the earth and the 

 heavenly bodies, the seasons and tides, the sun and the 

 wind and the rain, the weathering of the mountains, the 

 making of the fruitful land, and so forth. The reality 



