186 VETEEINARY STUDIES 



degree of immunity; but this immunity is gradually lost until 

 at two years of age nearly all are highly susceptible to the 

 disease. Cattle reared in the southern states on tick-free pas- 

 tures are as susceptible as those raised in the North. 



Period of incubation. — Tick fever usually develops in from 

 eight to ten days after direct inoculation of a susceptible ani- 

 mal with the blood of one infected, or that has acquired im- 

 munity from a previous attack. When infection occurs in the 

 natural way, a variable time elapses between exposure to tick 

 infestation and the development of the disease. In some cases 

 no evidences of the disease can be detected before from fifteen 

 to thirty — or even ninety — days after exposure. However, a 

 large percentage of cases develop within ten days after inocu- 

 lation. 



Symptoms. — It is frequently stated that tick fever occurs in 

 acute and chronic forms. The chronic form, however, often 

 follows the acute, and appears months after the acute attack. 

 These relapses or secondary attacks are not uncommon in the 

 late fall and early winter. It is then difficult to distinguish 

 them from ordinary debility from other causes except by the 

 history of a previous attack or by an examination of the blood. 



Fever. — In the acute type of the disease an elevation of tem- 

 perature is usually the first noticeable symptom. A tempera- 

 ture of 107 degrees or 108 degrees P. is not unusual, but 

 when it reaches 105 degrees or 106 degrees, other symptoms 

 usually become apparent. While there are considerable fluc- 

 tuations, temperature generally remains high during five to seven 

 days and may then drop suddenly to normal or below. Many 

 animals die during the extremely high temperature, or, if the 

 temperature falls, it is only as a prelude to death. The period 

 of subnormal temperature is a dangerous one, and collapse 

 should be fortified against ; otherwise an animal may succumb 

 that might by proper treatment have been saved. 



Other symptoms. — The patient usually stands apart from the 

 herd with head down and back arched, and in severe cases, or 

 when death approaches, it may lie or fall down. The pulse 

 and respiration are hurried. The urine may be highly colored 

 as port wine, or almost black, especially in fatal cases and when 

 near death. The red is coloring matter from the red corpuscles, 

 which are rapidly destroyed by the blood parasites (P. bigemi- 

 nwm). Other diseases producing bloody urine are rare among 



