364 



GENERAL PHYSIOLOGY 



But between the very slight power and rate of conduction 

 possessed by Orbitolites, and the very great power and rate 

 possessed by the nerve, there are found in the various living forms 

 the greatest variety of transitions. The cross-striated muscle-fibre 



f 



FIG. 157. Pseudopodium of Orbitolites. a, At * cut across ; b, effect of stimulation (formation 

 of protoplasmic globules) limited to the immediate vicinity of the place stimulated ; c-f, 

 transport of substance. The stimulated masses are transported along the pseudopodium to 

 the central cell-body, and their substance becomes gradually spread out (e, /) ; the unstimu- 

 lated protoplasm exhibits no phenomena of excitation but continues to flow centrif ugally . 

 and the pseudopodium soon lengthens again (e, f). 



conducts considerably more slowly than the nerve, the smooth 

 muscle-fibre still more slowly than the cross-striated, and so on. 

 Thus, according to the rate of conduction, living substances can be 

 arranged in a long series showing most delicate transitions. 



II. THE PHENOMENA OF CELL-STIMULATION 



After this general discussion of the individual elements of the 

 process of stimulation we can pass to the consideration of the 

 phenomena of stimulation themselves. 



Since the single cell does not allow the various vital phenomena 

 to be recognised with equal readiness, but according to its specific 



