148 



Bulletin 225. 



Fia. 31. — The carcass of an animal killed for beef 

 ehowing tuberculosis of the liver, omentum and 

 lungs. Generalized tuberculosis. 



coverers. It is also known 

 that when a healthy child 

 is exposed (infected) by 

 being brought in contact 

 with a child sick with diph- 

 theria, that the period of 

 incubation (that is, the time 

 elapsing between the ex- 

 posure and the time the 

 symptoms of the disease 

 appear), is but a few days, 

 and that the duration of the 

 disease is short, lasting but 

 a few days or weeks at the 

 longest. At the end of this 

 short period, the entire 

 course of the disease has 

 been rim and the child is 

 either dead or well on the 

 way to recovery. 



In tuberculosis we have 

 similar conditions, but they 

 differ in detail from those in 

 diphtheria in three very im- 

 portant points, — the length 

 of the period of incubation, 

 the way in which the specific 

 bacteria produce the dis- 

 ease, and the time 

 required for the dis- 

 ease to run its course. 

 With diphtheria the 

 specific bacteria pro- 

 duce a toxine which 

 poisons the system, 

 and tliis toxine is the 

 cause of death. In 

 tuberculosis the speci- 

 fic bacteria do not 

 produce such a 

 toxine, but they live 

 in one or more of the 

 tissues of the body, 



