92 HOG CHOLERA 



a screw clamp, enough virus is passed through the 

 system to eliminate danger from air bubbles, the 

 pinch-cock is closed, and all is ready to make the 

 injection. 



The vein into which the needle must be intro- 

 duced usually conforms roughly to the contour 

 of the outer margin of the ear, and is about one 

 inch removed from it. A spring clamp is ap- 

 plied near the base of the ear, thus compressing 

 this vein and rendering it plainly visible. The 

 ear is drawn taut with the left hand, and with 

 the right the needle is thrust quickly into the vein, 

 passed rapidly along its course about two inches, 

 and secured in position with the clamp which is 

 no longer needed to compress the vein at the base 

 of the ear. If the needle is properly in place there 

 will be a backward flow of blood through it. With- 

 out a moment's delay it is now necessary to con- 

 nect the needle with the supply of virus under 

 pressure, and to open the pinch-clock allowing the 

 virus to flow into the circulation. Otherwise the 

 hog's blood may clot in the needle rendering the 

 injection impossible. When the flow of virus is 

 established, one must see that the needle is re- 

 tained in place until the required quantity, al- 

 ready determined, has been injected. This will 

 require from four to thirty minutes, the time be- 

 ing governed by the degree of pressure applied, 

 by the size of the needle and the accuracy with 



