247 



prominent or marked in chronic cases or cases of long 

 duration. 



The heart, according to Smith, has the right ventri- 

 cle ''distended with blood, fluid or clotted, according to 

 the time elapsing between death and the examination. 

 The left ventricle is usually firmly contracted and may 

 contain a small quantity of fluid or clotted blood." The 

 small extravasations of blood under the epicardium and 

 endocardium are quite constant; they are most numer- 

 ous on the outside and inside of the left ventricle. 



WHAT IS IMMUNITY TO TEXAS FEVER ? 



IMMUNITY means that an animal is not susceptible to 

 Texas fever. It is now believed that an animal can ac- 

 quire immunity only by having the disease — one or more 

 attacks. One severe attack of the fever or two or more 

 mild attacks usually insure a safe immunity. 



Immunitv will last as long as the life of the animal, 

 if said animal becomes infested with ticks one or more 

 times each year of its life. But my observation of the 

 disease, as it occurs in native Alabama-bred cattle, leads 

 me to believe that immunity can be lost in two or three 

 years by keeping the animal free of all ticks. I am con- 

 fident that loss of immunity in this way explains the oc- 

 casional outbreak of Texas fever in herds that have been 

 kept free of ticks for two or more years, and then letting 

 the cattle become infested with ticks. 



METHODS OF PRODUCING IMMUNITY TO TEXAS FEVER. 



The natural method is the one in which the ticks do 

 the inoculating. Four different forms of tick inocula- 

 tions have been tried. In many instances Northern-bred 

 cattle were brought into the South, turned out with the 

 herd; permitted or forced to "rough it," and survive or 



