THE PROCESS OF EXCITATION 



107 



responsivity. The nerves and muscles of the animal retain their 

 excitability for even a longer period under the same conditions. 

 Indeed, we have histological evidence of the existence of organic 

 reserve material in the various cells in the form of embedded 

 bodies in the protoplasm. As for instance the disappearance of 

 the Nissl granules in the ganglion cells following great activity/ 

 (Figure 12), or that of the granules in infusoria cells during 

 starvation.^ (Figure 13.) We assume that a certain amount of 



A B 



Fig. 13. 

 Paramecium aurelia. A— In nonnal state. B— In a state of starvation. 



organic foodstuffs in a state properly prepared is present in the 

 cell. As the amount of these prepared substances is consumed, 

 new quantities of stores, having undergone various preparatory 

 processes, among which the enzymic actions may be considered 

 to play a chief role, are brought into that form in which they 

 appear suited to fill the gap produced by disintegration. Plant 

 physiologists in particular have here again furnished us with some 



1 Gustav Mann: "Histological changes induced in sympathetic motor and sensory 

 nerve cells by functional activity." In Journ. of Anat. and Physiol. 1894. Further; 

 Gordon Holmes: "On morphological changes in exhausted ganglion cells." Zeit- 

 schrift f. allgem. Physiol. Bd. II, 1903. 



2 Wallengren: "Inanitionserscheinungen der Zelle." Zeitschrift f. allgem. Physiol. 

 Bd. I, 1902. 



