336 GENERAL PHYSIOLOGY 



found, e.g., in the brains of idiots, " petrified " ganglion-cells in the 

 true sense of the word (Fig. 149, B). 



Besides the forms of metamorphic processes here presented, 

 pathology recognises others, such as pigment-atrophy, hyaline 

 degeneration, colloid metamorphosis, etc., at the basis of which 

 there is always the same principle, namely, that the meta- 

 bolism of the cells takes a perverse course, and forms substances 

 that normally are formed either not at all or only in slight quantity, 

 the final result being the death of the cell. But in the cases 



FIG. 149. Calcification of cells. A, Calcified cells in the wall of a blood-vessel. B, Calcified 

 ganglion-cells from the brain of an idiot. (After Ziegler.) 



mentioned these substances and their genesis are much less known 

 than in the metamorphic processes that have been discussed ; 

 hence it does not appear necessary in this place to go into 

 them more fully. 



In general, metamorphic processes, especially the genesis of the 

 substances that arise in them and the disturbances of normal 

 metabolism upon which they rest, need greater elucidation ; 

 naturally this will come in proportion as the knowledge of meta- 

 bolism in general becomes extended. 



B. THE CAUSES OF DEATH 



The causes that lead to death are as manifold as are its 

 phenomena. We have already touched here and there upon some 

 of the special causes, but it is impossible to treat these in every 

 individual case. It is necessary, however, to go somewhat more 

 fully into the general causes, because with them is joined the 

 interesting question whether death is for all living organisms the 

 dira necessitas that it is for mankind in other words, whether 

 there are organisms whose bodies are immortal. 



