6oo Veterinary Medicine. 



The womb will at times show petechiae and in pregnant cows 

 the foetus will show sero-sanguineous effusions or even extravasa- 

 tions in the chest or abdomen, and hsemoglobinuria (I^ignieres). 



Incubation. Outbreaks occurring in the North, in herds into 

 which southern infected cattle have been brought, were at first 

 held to indicate an incubation of thirty or forty days (or even 

 sometimes sixty-five), but this is now explained by the time re- 

 quired for the laying and hatching of the eggs of the mature 

 ticks and the evolution of infecting young larval or seed ticks. 

 The actual incubation, as shown by the subcutaneous or intra- 

 venous injection of the blood of an infected ox, extends from 

 three to ten days. The hyperthermia is usually shown on the 

 third day, and the more manifest outward symptoms on the sixth. 

 Extreme heat of the weather, a special susceptibility of the ani- 

 mal infected, and especially a large dose of the blood and proto- 

 zoa will hasten somewhat the onset, but three to six daj-^s may be 

 set down as the rule after the ticks have introduced the parasite 

 into their victim. Cattle taken from the northern states and 

 placed on southern pastures, or passing over trails already well 

 stocked with the ticks, are infected at once and sicken in from 

 three to ten days. Cattle in their northern home placed on a 

 previously uninfested field with southern cattle just arrived, do 

 not suffer for thirty, forty, sixty, and in exceptional cases, even 

 ninety days. The paradox is explained by the time wanted for 

 the laying of the eggs and the hatching of the tick larvae. The 

 female tick does not lay eggs until she is fully mature, and if the 

 ticks on a southern ox are still immature there is a variable 

 period of delay until the eggs are mature enough to be deposited. 

 Then the ovigerous tick drops off her host and spends one week 

 in laying her eggs. In warm weather these eggs take three to 

 four weeks to hatch, so that usually five weeks elapse before the 

 young (seed ticks) can climb upon the ox and infect him. Add 

 three to six days more for the actual incubation and we ac- 

 count for about six weeks of delay in the appearance of the 

 disease in northern cattle. If we consider further that a wet sea- 

 son occurring after the eggs have been laid and before they are 

 hatched tends to divest them of their protective covering and to 

 expose them to destruction, and that, in any case, a cold season 

 will delay the hatching until the recurrence of warm weather 



