94 HOG CHOLEEA 



causing it to prick through the wall so that virus 

 will escape from the vein and accumulate in the 

 surrounding tissues when it is applied under pres- 

 sure : if the needle tends to pucker the skin at the 

 point of entrance, dampen both needle and skin 

 (an atomizer containing alcohol is convenient for 

 this purpose). In inserting the needle hold the 

 index finger of the right hand well toward the 

 point, between the ear and the needle; it is im- 

 possible to guide a needle when it is grasped at 

 the nub only: if when pressure is applied virus 

 is seen to escape from the vein and accumulate in 

 the surrounding tissues, release the pressure at 

 once ; otherwise all chance of entering the vein in 

 subsequent trials will be destroyed. 



Before inserting the needle some operators 

 connect it directly to the rubber tubing containing 

 the virus under pressure, thus obviating annoy- 

 ance incident to blood clotting in the needle or to 

 accidental breaks in the slip connection due to 

 struggling on the part of the hog. When this 

 technique is employed one must depend largely on 

 his sense of touch to determine when the needle 

 is in position, for backward flow of blood cannot 

 be observed. In case of doubt as to whether the 

 needle has entered the vein, one may compress the 

 tubing between the pinch-cock and the needle, at 

 the same time observing whether the virus thus 



