250 



blood cells is greater in the young tlian in tlie older 

 animals. This may be due to the fact that there is a 

 relatively greater (juantity of red marrow in the young 

 animals, and this red marrow tends to reproduce red 

 blood cells nearly as fast as they are destroyed by the 

 micro-parasite. The general vigor of a young animal 

 may add to its resisting and recuperating ])()wer. More- 

 over, it is well-known that young animals exhibit greater 

 power of repairing wounds and recovering from almost 

 any disease than older ones. Broken bones unite quicker 

 and better in 3'oung animals than in mature ones. As 

 Dr. Francis remarks, this method of immunizing suck- 

 ing calves is a good and safe way for farmers who buy 

 a few animals; but where many animals are wanted for 

 a large ranch it is cheapest to use the defibrinated blood 

 method. One drawback to immunizing calves is that 

 the owner must wait one or two years before the calves 

 develop into breeding animals; it means loss of time, 

 but is a safe method. 



The Defebrinated Blood Method of producing im- 

 munity to Texas fever in cattle was originated or dis- 

 covered in Australia. It has been most extensively em- 

 ployed i nthis country by Dr. Connoway of the Missouri 

 Experiment Station, and Dr. Francis of the Texas Ex- 

 periment Station. It has been tested by the Bureau of 

 Animal Industry at Washington, D. C, and by the Louis- 

 iana, the Mississippi and the Alabama Experiment Sta- 

 tions. 



Brefly speaking, it consists in inoculating a suscepti- 

 ble or non-immune animal with blood that is freshly 

 drawn from an immune animal and defebrinated. The 

 animal from w^hich the blood is derived should be at 

 least two j^ears old, and Southern-bred, and known to 

 have had ticks upon it some time during the second sum- 



