194 THE COLLECTION OF MATERIAL 



preparation of serum (p. 48). When a small quantity only of blood is 

 wanted a syringe is used instead of a trocar. 



Guinea-pigs. 



Guinea-pigs may be bled from the jugular vein, from the femoral or carotid 

 arteries, or by cardiac puncture. 



A. From the jugular vein. For the anatomical data see p. 172. 



1. Fix the guinea-pig on its back with the head extended. Shave the 

 skin over the front of the neck and cleanse it in the ordinary way. 



2. Make an incision through the skin and sub -cutaneous tissue along the 

 line of the vein, dissect away the cellular tissue with a director and the vein 

 will come into view. 



3. Pass the needle of a sterile syringe or the end of a pipette (similar to that 

 described at p. 166) very obliquely into the vein. If a slip knot be passed 

 under the vein with a Deschamps needle on the cardiac side of the puncture, 

 the vessel can be compressed and the flow of blood into the pipette facilitated. 



4. Having collected the blood, withdraw the needle or pipette and make 

 certain that there is no haemorrhage from the puncture. If the vein be 

 bleeding, tie a ligature above and below the puncture. Put two or three 

 stitches in the skin and cover the wound with collodion. 



Note. The blood may be collected directly in a sterile tube or flask by passing 

 a fine trocar into the exposed vein. The operation in this case is described at 

 p. 49. 



B. Carotid and femoral arteries. 1. Expose the vessel (pp. 173 and 174). 



2. Puncture the wall of the artery obliquely with a syringe needle, the 

 end of a bent pipette or a small trocar. 



3. Having collected the blood, withdraw the instrument, stitch up the skin 

 and paint the incision with collodion. 



Sometimes haemorrhage occurs when the needle is taken out of the artery. This 

 can be guarded against by placing two ligatures beneath the vessel, one above and 

 the other below the puncture, then, if haemorrhage occur, the two threads can be 

 tied and the wounded part of the vessel isolated. 



C. Cardiac puncture. Cardiac puncture as practised in physiological 

 laboratories may be usefully applied for bacteriological purposes (Pagniez). 

 It allows a much larger volume of blood to be collected than is possible by 

 other methods, is easily performed and is unattended by danger to the animal ; 

 moreover the blood is not exposed to any risk of contamination. The tech- 

 nique, which is as follows, has been worked out by Raybaud and Hawthorn. 



1. Tie down the animal on its back, shave and cleanse the skin over the 

 front of the cardiac area. Have ready a sterile syringe capable of holding 

 5 c.c. and fitted with a needle of the ordinary pattern but very sharp. 



2. At a point on the left margin of the sternum, about 8-10 mm. above 

 the angle formed by the base of the xiphoid cartilage and the last rib carti- 

 lage articulating with the sternum, push the needle sharply to a depth of 

 15-17 mm. above the last but one or last but two chondro -sternal articulations. 



The needle will pass into the left ventricle, and by inclining it a little towards 

 the middle line it can be made to enter the right ventricle. This method is to be 

 recommended because the risk of wounding the anterior margin of the left lung is 

 lessened, and if the heart were punctured at a higher level than that described the 

 auricle would be penetrated and ruptured. 



3. Fill the syringe slowly with blood, and withdraw the needle sharply 

 and quickly. 



Rabbits. 

 A. The ear veins. The simplest method of collecting blood from a rabbit 



