226 THE ACTION OF THE LIVING CELL 



although in general little definite commitment has 

 been made as to the exact nature of this response. Such 

 a migration of leucocytes is found to take place fol- 

 lowing any kind of tissue injury, such as mechanical 

 mutilation or the application of irritating chemicals 

 such as chloroform or croton oil, as well as after bac- 

 terial infection. It would seem, therefore, that the 

 specific nature of the cause of injury is of no impor- 

 tance in determining the migration of the white cells, 

 but that an endocellular substance liberated from the 

 tissues is responsible for the chemotaxis. 



It is possible that cytost may be such a substance, 

 for we have frequently observed an increased leu- 

 cocyte count in animals at short intervals following 

 the injection of extracts of autolyzed tissue. This ob- 

 servation suggests that the migration of leucocytes to 

 the site of infection is brought about by the cytost 

 liberated from the tissues of the host by the activities of 

 the invading organisms. 



We have shown elsewhere in the text that when 

 present in appropriate concentration cytost stimulates 

 the rate of proliferation of cells. With this in mind, 

 it seems likely that the connective tissue barrier which 

 is thrown about a localized infection may result from 

 the stimulus afiforded by the cytost liberated by bac- 

 terial action. 



From the above it should be clear that as a result 

 of bacterial infection cytost may be liberated, and in 

 consequence the animal may sufifer from a cytost in- 

 toxication as well as from the specific disease en- 

 gendered by the bacteria. The liberation of cytost in 

 this manner may cause serious consequences, or it may 

 stimulate the defense mechanisms of the host in such 



