88 THE farmer's veterinarian 



acts in live stock. If an animal is inoculated with 

 Texas fever germs, the veterinarian knows the 

 course of the disease beforehand. In a general way, 

 he knows when the fever will begin, how long it 

 will last, when it will be at its highest point, and 

 when it will disappear. He knows all of this, even 

 before he makes the inoculation. Yet no disease 

 invariably runs the same course in different in- 

 dividuals. In fact, the virulence of bacteria have 

 much to do with the course ; mild cases occur 

 usually when the germ is weak, and severe cases 

 when the germs are very virulent. This explains 

 why some attacks of measles or Texas fever or hog 

 cholera are more fatal than other attacks in other 

 places, or at other seasons of the year. 



Typical Courses the Rule. — It is in rare cases 

 only that a regular course is not followed by most 

 diseases. Take an infectious disease. The period 

 of incubation comes first ; this follows up the in- 

 fection. During this period, no change in the 

 animal is observed. He seems well, acts well, and 

 does his work well. Nevertheless, all the time, 

 during this period of infection, the germs are de- 

 veloping, multiplying, gaining headway, and so 

 entrenching themselves that illness and disorder 

 will soon follow. The period of infection varies 

 in different animals and in different diseases. It 

 may take two or three weeks for development, or 

 as few as two or three days. 



Following the period of infection comes the 

 period of eruption. At this stage the typical char- 

 acteristics are observed. At the next step the dis- 

 ease reaches its height with the animal under its 

 complete dominion. But only temporarily. If 

 properly nursed and treated, with most diseases, 

 the animal will pass through the period and recover. 



