249 



tection from cold nights and rains. Some losses occur 

 by this method, and it is a little more inconvenient and 

 uncertain than either of the two methods that will be 

 mentioned following this. 



The fourth modified form of tick inoculation is the 

 one where sucking calves, 2 to 4 months old, are brought 

 into the South in the fall or winter or early spring, and 

 allowed to take milk from a Southern-bred cow or are fed 

 fresh sweet milk from a Southern cow. While young 

 and during the time before it is weaned, put a few seed 

 ticks upon the calf or permit them to get upon it in small 

 numbers. Natural tick inoculation will then occur when 

 the calf is best able to resist severe fever and to recover 

 from it. It is possible that the milk of a Southern-bred 

 immune cow may have some immunizing power, but I 

 doubt it. I think the milk of a non-immune cow would 

 be as effective because it keeps the calf in the best of 

 condition to resist, and to recover from, the fever or at- 

 tack of the micro-parasites upon the red blood cells. It 

 is a well-known fact that young calves or cattle do not 

 have Texas fever in as severe a form as do older or ma- 

 ture cattle. All competent observers or investigators 

 of Texas fever have noted that fact. According to Hunt 

 of Australia, (who produced by inoculation the fever in 

 calves born of immune cows) , immunity is not inherited. 

 It is very probable that all Southern-bred calves do not 

 inherit immunity, but acquire it after birth by tick in- 

 oculation. No doubt that the vast majority of South- 

 ern-bred calves have the fever in such a mild form that 

 it is not appreciable. This partial immunity of 

 calves to the fever may be explained by the fact that 

 young animals have a greater number of red blood cells 

 per cubic millimeter than do older animals, and can 

 carry on the functions of the blood better in case of loss 

 of red blood cells. Also, the power of reproducing red 



