Physiology of Pathogenic 31icrobes. 81 



appreciable. A preparatory period then ensues dur- 

 ing which the microbe proliferates, multiplying its 

 means of action upon the economy. This period 

 corresponds to the incubation. It is shorter the bet- 

 ter the organism is adapted to the life of the germ; 

 its duration also varies with the nature of the germ 

 and its virulence, with the abundance of the virus, 

 with the receptivity of the subject, the place of inoc- 

 ulation, etc. In some diseases the duration of the 

 incubatory period is almost constant; in others it is 

 very variable (rabies). 



Certain diseases have several successive incuba- 

 tions, or, rather, latent periods, during which the dis- 

 ease germ ceases its activity, slumbers, to resume at 

 a later period its course of invasion (tuberculosis, 

 dourine, syphilis). The organism is then in the con- 

 dition of latent microbism. 



The period of incubation is completed when the 

 first manifestations of the morbific action of the virus 

 appear; the premonitary symptoms are in no way 

 characteristic ; yet, in the course of an epizootic, 

 there are certain signs by which we can recognize 

 the invasion of the disease in an individual previously 

 healthy. Thus, a persistent fever in one of the cattle 

 of a stable where pleuro-pneumonia prevails, would 

 excite a suspicion of its invasion by this disease. 



The early obscure symptoms more or less quickly 

 give place to troubles more and more serious, which 

 clearly characterize the affection with which we have 

 to do, and express the influence of the progressive 

 action of the microbe. This is the period of increase. 

 We will not enter here into details of the common 

 symptoms of microbic diseases, an outline of which 



