150 



WITHROW MORSE. 



Interesting as these instances are, relatively meagre investi- 

 gation has been made as to the causes and factors involved in the ' 

 physiology of the process. On the other hand, such studies as 

 have been made have borne good fruit. It was in the studies of 

 ctenophore larvae that Metchnikoff conceived the idea of what 

 later became the theory of phagocytosis. Later this investiga- 

 tor studied the cytology of the larval frog's tail during the stages 

 of metamorphosis. Extensive morphological studies have been 

 made upon the stages of metamorphosis in insects. The changes 

 which the salmon undergoes in breeding season have likewise 

 received considerable attention. 



Passing from the natural atrophy found in such instances as 

 these, to what is termed pathological atrophy, we encounter the 

 processes of progressive muscle atrophy, acute yellow atrophy of 

 the liver and other states which bear many features in common 

 with certain of the so-called natural atrophy processes, and this 

 is true to such an extent in regard to the atrophy of the muscles 

 of the larval frog at metamorphosis and the conditions observed 

 in progressive muscle atrophy or Zenker's degeneration that it 

 is difficult to believe that we are dealing with fundamentally 

 different physiological processes. 



The purpose of the following communication is to attempt to 

 show that there are certain factors involved in the atrophy of the 

 tadpole's tail which are to be considered as causal or of primary 

 importance as conditions; and the similarity in cytological pic- 

 tures and in certain known conditions in this case and in thac of 

 pathological atrophy makes it fairly probable that we are dealing 

 with the same physiological factors, so that we encounter here 

 an instance where the comparative physiology of a lower form 

 of organism sheds light upon the economy of the higher organisms 

 of especial interest to the pathologist. 



HISTORICAL. 



Although Metchnikoff had witnessed the activity of phagocytic 

 cells earlier, in the larvae of errantiae, his first report involving the 

 conception of cells wandering in the body fluids of one organism 

 and serving as scavengers was made in 1883 (2). Early in the 

 history of the problem, this investigator recognized the practical 





