THE RELATION OF BACTERIA TO DISEASE 67 



Bacterial poisons, it might be said, usually express 

 some definite predilection for special organs or tissues. 

 For instance, the tetanus toxins attack the brain. The 

 streptococci attack red blood cells, and the typhoid 

 bacillus settles in the lymph glands of the small 

 intestine. 



Incubation. After bacteria have gained their foot- 

 hold there is a certain lapse of time until their effects 

 become evident. This is the incubation time. Its 

 length depends upon the number of organisms enter- 

 ing, their virulence, and the resistance of the body. 



Mixed Infection. Sometimes there is more than one 

 kind of bacterium in an infection. This is called a 

 mixed infection, and although there is the expression 

 of both causes, one usually predominates. This 

 usually results from the entrance of the second invader, 

 owing to the lowered resistance of the body produced 

 by the first invader. 



Transmission of Disease. The transmission of dis- 

 eases from one individual to another takes place 

 in various ways, but it may be said in general that 

 the means of transference must present conditions 

 favorable for the retention of virulence on the part 

 of the bacteria. Some bacteria, notably gonococci and 

 influenza bacilli, die very quickly when dried or 

 exposed to direct light. On the other hand, tubercle 

 bacilli resist drying and diffuse light for several days. 

 Coughing and spitting transfer infective organisms 

 from the mouth to the air, and persons in the vicinity 

 may receive them. Clothes soiled with discharges, 

 both urine and feces, from typhoid patients, contain 

 the bacilli and are capable of carrying the disease. 



