THE EFFECT OF EXTERNAL INFLUENCES ON CELLS 65 



Indeed, in many plants one may observe that on a sunny day the whole course 

 of the sun is followed by appropriate movements of the plant. This effect is 

 brought about chiefly by the more strongly refractive rays of the spectrum. 



Galvanotropism. With long exposure to a constant current root tips turn 

 toward the cathode. 



Even in the highest animals we meet with extensive regenerative proc- 

 esses which, in part at least, are caused by a kind of chemical stimulation. 

 Thus if a large part of the liver be cut away, a considerable regeneration of 

 liver tissue follows (Ponfick, Podwyssozki). After extirpation of one kidney, 

 the remaining kidney increases considerably in volume by new formation 

 of kidney tissue. Numerous discoveries of the pathologists on abnormal 

 growths belong here also. 



Among the Mammalia, however, the powers of regeneration are relatively 

 small in comparison with those of the lower vertebrates and especially of 

 certain invertebrates and of plants, for in the former the tendency to regen- 

 eration is limited to certain tissues, while in the latter whole organs may be 

 formed anew. 



The tendency to the syntheses of nonliving substances in the organism 

 appears to be favored to a certain extent by a rich supply of food. In an 

 atmosphere rich in C0 2 , under otherwise similar conditions, plants show a 

 greater production of starch; and with an abundant supply of carbohydrates 

 animal cells form fat which is stored up in the fat cells. Animal cells 

 carry on also a multitude of other syntheses the stimulus to which might well 

 be sought for in a chemical excitation effected by the substances supplied them. 

 Anything more exact than this is quite beyond our knowledge at this time. 



K. PARALYSIS AND FATIGUE 



We meet with a true case of paralysis when a dissimilative stimulus is 

 carried beyond a certain strength. This is true of all kinds of stimuli and 

 for all kinds of cells, in so far as they can be roused to a state of activity 

 by the particular stimulus. If the strength of the stimulus be not too great, 

 nor its duration too long, complete restoration may take place after its 

 cessation.- But if the stimulus be too strong or if it last too long, it has a 

 fatal effect on the protoplasm. 



Certain chemical substances e. g., the narcotics, to which belong alcohol, 

 ether, chloroform, morphine, cocaine, paraldehyde etc. are characterized by 

 their paralyzing effects, obtained even with small doses. After a short period 

 of excitation, the protoplasm exposed to these substances loses to a greater or 

 less extent its vital activity. With small doses and short exposure the paral- 

 ysis passes off, but with large doses or long exposure the paralysis becomes 

 more and more profound until death finally ensues. 



Fatigue may be considered as a special kind of paralysis. In all living 

 beings (though in different genera and individuals in different degree) there 

 always occurs after a sufficiently intense dissimilative activity a reduction 

 of the functional power, as a consequence of which the same strength of 

 stimulus produces a much weaker effect than before. If the stimulation be 



