INFECTIONS. 9 



organism. This period is known as the "incubation period, " and 

 varies according to the biological characters of the infecting or- 

 ganism, but is also influenced by the number and virulence of 

 the organisms and the individual susceptibility of the host. 



The course of a disease is determined by conditions produced 

 by the specific organism and partly by the distribution of these 

 organisms. But even here it is to be noted that the course of 

 the disease varies. Many of these variations we are by no means 

 able to explain. 



The symptoms and signs produced by an organism will vary 

 as the organism acts locally or generally. In local infections 

 the most marked disturbance occurs at the portal of entry of the 

 microorganism, while in general infections the reaction manifests 

 itself in all, or a large part, of the body. The infecting microor- 

 ganism may produce disease either in a mechanical way because 

 of large numbers, or, as is the case of most all infections, because 

 of toxins which may act locally or be distributed over a large part 

 or the whole, of the body. Some organisms, as the bacilli of diph- 

 theria and of tetanus, produce extracellular toxins, while other 

 organisms, as those causing typhoid fever and cholera, have 

 intracellular toxins which are liberated supposedly when the 

 organisms disintegrate. 



After organisms have entered the body the distribution varies 

 with the species. Thus we see that staphylococci form furuncles, 

 carbuncles and pustules in localized areas, typhoid bacilli though 

 causing lesions in the intestine are usually present in "the blood 

 stream, while the tetanus bacilli form a toxin which is distributed 

 through the entire body. At times microorganisms do not remain 

 localized at the portal of entry but pass on to the lymphatic 

 glands and other parts of the body, here producing pathological 

 conditions. In some infections the microorganisms gradually 

 involve more and more of the tissues of the body. Microorgan- 

 isms may first lodge in one part of the body and produce disease 

 in that part and from these primary lesions, other parts of the 

 body may become infected. When the blood stream is not only 

 the carrier of microorganisms but becomes the place for growth 

 and reproduction of the same, a septicaemia arises. While almost 

 any of these conditions may be produced by any of the pathogenic 

 bacteria, still certain organisms are more likely to produce one 



