IMMUNIZATION OF CATTLE 591 



of the disease, and afterward, immunty just as effectual as when 

 the blood is taken from an immune animal immediately before being 

 used. 



"We have not as yet found any way of preserving the blood drawn 

 from the vein for any considerable time without its losing its power 

 to produce immunity." 



The Louisiana report of Dalrymple gives the following conclusions 

 and directions as to the immunizing of Northern cattle by the use 

 of fresh blood from infected animals: 



"Previous to the discovery and adoption of the blood-inoculation 

 method of immunizing susceptible Northern cattle against the ravages 

 of Texas fever the mortality in these animals ranged anywhere 

 from 40 to 90 per cent. This, necessarily, discouraged Southern 

 stockmen in the importation of pure-bred cattle for the purpose of 

 improving their herds, and accounts, mainly, for the scarcity of 

 pure and highbred stock in the South up to within recent years. 



"Consequent upon the use of this artificial method of immuni- 

 zation, however, the death rate from the fever has been enormously 

 reduced. In a bulletin issued by the Texas Experiment Station in 

 1902 a record was compiled showing the percentage mortality of 

 inoculated cattle that had been treated at the Texas, Louisiana, and 

 other Southern (including Missouri) stations, which comprised several 

 thousand head (4562 up to January 1, 1904), to be only 7.7, and 

 that, too, under various conditions of treatment after they had 

 been placed in their owner's care. This record has given increased 

 encouragement to cattle men in the South. 



"The technique of the operation as practised in the Louisiana 

 Experiment Station is the following: The supply animal from 

 which the immunizing infected blood is used is either a native or 

 a Northern immune which should be in robust health and condition. 

 Experiments and experience seem to indicate that the most suitable 

 subjects for immunization are cattle from eight to twelve months old, 

 in good flesh, and weight from 500 to 800 pounds. Before inoculation 

 it is well to allow the animal to rest for a few days, especially those 

 that may have come off a tedious railroad journey; and during this 

 time they should be well and carefully fed and kept absolutely free 

 from ticks. 



"The operation seems more easily performed with the supply 

 animal thrown down and tied. The hair is clipped from a portion 

 of the skin of the neck just over the jugular vein. The denuded part 

 is bathed with an antiseptic solution. The neck of the animal is 

 now straightened and tensed, and a piece of strong cord or small 

 rope tied around its base sufficiently tight to check the flow of blood 

 and raise the vein. A small trocar and cannula, or hollow sharp- 

 pointed needle, which has previously been sterilized, or disinfected, 

 is then inserted into the distended vein and is directed up the vessel 

 toward the head. As soon as the needle enters the vein the blood 



