THE PHENOMENA OF INFECTION 89 



and this throws an increased burden on the 

 body cells. In some diseases phagocytosis 

 plays an important role. It must be evident 

 that the engulfment of bacteria by phagocytes 

 is a more conservative method of disposing of 

 the invading cells than their extracellular de- 

 struction, since in the former the body is pro- 

 tected against the poison liberated by bacterial 

 cleavage. Nothing more dangerous to the in- 

 fected individual could happen than the sud- 

 den cleavage of all the bacteria in his body. 

 The poison liberated in this process would 

 overwhelm him at once. This is a probable ex- 

 planation of the fact, already referred to, that 

 the case mortality in typhus fever is higher 

 among the well nourished than among the less 

 robust. Bacterial cells, as well as body cells, 

 have means of protecting themselves. The tu- 

 bercle bacillus through limitless generations of 

 parasitism has developed coatings of fats and 

 waxes which protect it against the action of 

 secretions of body cells quite as efficiently as 

 coats of mail protected our ancestors against 

 the weapons of their time. Moreover, bacterial 

 cells may develop increased resistance or be- 

 come to some extent immune to the action of 

 body cell secretions. Occasionally bacteria per- 

 sist in the body for long periods after recovery 



