DISEASES OF THE BLOOD. 115 



produced to act as a prophylactic. When the morbific 

 organisms are hardy and capable of withstanding con- 

 siderable variations in life conditions so that animals of 

 very different kinds are invaded by them, the disease which 

 they produce is panzootic ; foot-and-mouth disease is a 

 good illustration of this. Our diagnosis of these specific 

 disorders generally must be prompt, to check any tendency 

 to spread. In all cases where any doubt exists the animal 

 must be isolated as suspicious, and other prophylactic 

 measures adopted. Diagnosis is often followed by the 

 stringent test of accuracy of opinion which immediate 

 slaughter affords. Fortunately, therefore, these disorders, 

 especially the most acute of them, are ushered in by con- 

 siderable rise in temperature. This occurs very shortly 

 after introduction of the poison into the system, and before 

 it has had much time to multiply therein and to become 

 expelled into the air around, or with the excreta. This rise 

 is the first indication of the fever which constitutes the 

 systemic disturbance in all these cases. Later the general 

 signs of fever are manifested, and they run their course 

 for some time before any local manifestations of disease 

 are shown. Indeed, the latter in some diseases (exanthe- 

 mata) seem to constitute a crisis generally of a favorable 

 character. In all cases, then, febrile symptoms, more or 

 less acute, usher in an attack, and constitute the pre- 

 monitory indications of disorder. Only when we are 

 aware of the prevalence of a specific disease are we, in 

 the first stage, able to surmise the nature of the coming 

 disease, for the fever does not differ from ordinary pyrexia. 

 Only when local lesions occur can we complete our diag- 

 nosis, and we shall generally be able to find some patho- 

 gnomonic symptoms. It will be observed that the virus in 

 these specific disorders almost always like an eliminative 

 medicinal agent enters the blood, causes certain changes 

 in that fluid, and then is removed by some tissue or other. 

 And as different medicines are severally removed by tissues 

 on which they exert their special action, so in specific 

 disorders we find that in epizootic eczema the feet and 

 the mouth are affected, in pleuro-pneumonia the lungs, and 



