550 Veterinary Medicine. 



g. In the Gulf states, in stables which the cattle occupy con- 

 stantly or enter twice daily for milking or feeding, the ticks may 

 live through the entire winter. The same has occurred in the 

 warm swill stables in the north. 



10. When taken into a new locality, it is rarely the mature 

 ovigerous ticks that bite and infect the native cattle of the place, 

 but the next generation of larvae, so that time must be allowed 

 for the laying and hatching of ova. 



11. Ovipositing usually occupies about a week, while hatching 

 varies with the temperature from two to six weeks. 



12. Ca.ses can be adduced in which native cattle followed, on 

 the same pasture, the tick-bearing infecting cattle, and remained 

 for a week or more, and yet escaped, the larvae being as yet un- 

 hatched from the ova. Other native cattle, following these two 

 or three weeks later, perished almost without exception. 



13. This delay in the hatching may be indefinitely prolonged, 

 and thus in the southern states, the winter may be tided over, 

 without the loss of vitality in the ova, especially if it is covered 

 by leaves, moss, wood, or decaying vegetable matter. 



14. When dealing with lung plague in Chicago in 1888, I 

 noted the facts that every cow that entered a city stable through 

 the stock yards during the dry, hot, midsummer weather died of 

 Texas fever within a month, while those that passed through 

 the .same yards during a particular rainy week, all escaped. 

 Berkau has shown that, in the absence of the coating of the 

 glutinous saliva, the eggs do not hatch, and here we may assume 

 that this covering was washed off by the rains and the eggs 

 perished. 



15. It has long been noticed that the ticks are scarcely at all 

 dangerous to young calves living on milk. This applies not only 

 to calves born of cows native to infected localities, and therefore 

 possibly having a congenital immunity, but also to the calves 

 of northern and susceptible cows, and which were exposed 

 simultaneously with their dams. It suggests a .special defensive 

 power in even the bovine system when sustained on animal food. 

 In the Bureau of Animal Industry experiments, calves of four 

 months, already using vegetable food freely, .sickened but still, 

 as a rule, recovered. 



16. The Bureau fed three cattle with adult live ticks (2000 to 

 one animal) but no infection resulted. 



