CHEMICAL CEPTORS 101 



one of which is the colon bacillus. By the production 

 of gas these bacteria aid the peristaltic movements of 

 the intestines and the movements of the diaphragm, 

 in the acts of breathing, talking and vomiting for 

 which resilient abdominal contents are necessary. On 

 the other hand, it is probable that the bacteria them- 

 selves have had a selective influence on the modifica- 

 tion of the intestines and abdomen perhaps even 

 of food itself to meet their own life requirements. 

 So intimate is this reciprocal relation that, like the 

 insects and the flowering plants, like the rhinoceros 

 and the rhinoceros bird, man and his gasogenetic 

 bacteria form a strange partnership for mutual profit. 



Disturbed Symbiosis and Disease 



These symbiotic relations, normally so useful to 

 man, may be easily disturbed and cause disease or 

 "infection" -a triumphal adaptation for the bac- 

 teria at the expense of man. It is but a step for these 

 bacterial residents from a temperate diet of cell secre- 

 tion in time of health to an intemperate consumption 

 of cell substance itself, when the resistance of the host 

 is low. Thus the diphtheria bacilli, normally resident 

 in the throat, may turn upon their cellular benefactors 

 and run riot in diphtheria. Thus the pneumococci, 

 constantly present in the pulmonary tract, may attack 

 the source of their food supply and cause pneumonia. 

 Thus the bacteria of the nose may attack its membrane, 

 the secretion of which they subsist upon, and cause 

 a cold ; or the colon bacilli, normally resident in the 

 intestine, may suddenly attack the peritoneum, when 

 the condition of the appendix is such as to reduce its 



