62 THE RELATION OF BACTERIA TO DISEASE 



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. The 

 local gross effects of bacterial invasion are expressed in 

 inflammation, which is greatest in those which act by 

 their mechanical presence in a confined locality, usually 

 aided by some of the poisons mentioned above. 



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 

 diseases' 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. 

 Scales from the skin in the acute eruptive diseases of 

 children may transmit infection. Milk and water 



