THORACIC DUCTS. 367 



uniting witli tlie duct from the tliorax. The lymph in these vessels 

 will be pale, and hence they must be looked for with care. They 

 may usually be recognized from their characteristic moniliformi 

 appearance (Fig, 103j ; they may be injected (§ 992, A). 



LYMPHATIC VESSELS. 



The lymphatics, like the veins, coutain many valves, making it impossible to inject 

 from a large trunk peripherad, as with the arteries. The vessels may be filled, however, 

 by the puncture method of Liidwig, which consists simply in thrusting a sharp pointed 

 canula into the tissues and forcinsr Berlin blue through the canula with a syringe. 



§ 992. Lymphatics of the Arms and Legs. — To inject these 

 prepare a glass canula (Fig. 32), leaving the point sharp. Fill the 

 syringe with Berlin blue and connect it by means of a rubber tube 

 to the canula. Then with the tracer perforate the skin covering the 

 pad in the middle of the hand or foot of a cat just killed (see §§ 189- 

 194), and insert the canula. Push it into the tissues slightly and 

 force the piston slowly down ; at the same time compress the foot 

 and press upon the limb in such a way as to facilitate the flow of 

 the mass centrad. It is well to insert the canula into all the pads 

 on the ventral surface of the manus or pes. It requires some time 

 to fill the vessels well. In the cat the larger trunks follow the veins. 

 If the leg is pressed as directed and the injection long enough con- 

 tinued (15-30 minutes), the thoracic duct may be filled. 



§ 992, A. Lymphatics of the Neck and Face. — To inject these employ a similar or 

 the same specimen, and insert the canula in the naked place at the end of the snout, as 

 directed for the pad of the foot. Press on the nose and face. In this way the lymphatic 

 vessels on the face and in the neck and the lymphatic glands in Fig. 87 {Gl. lym.) are very 

 easily injected. 



§ 992, B. Injection of Lymphatic Glands. — The lymphatic glands upon an injected 

 vessel are injected, since the vessels enter them. One may, however, inject the glands 

 directly and so fill the efferent vessels. This is very easily done by inserting the canula at 

 the peripheral edge of the gland and injecting centrad. The gland will first become very 

 blue and then the mass will appear in the efferent vessels. Those at the side of the face 

 (Fig. 87) and the mesenteric glands (§ 731) are large and favorable for this operation. 



If it is desired to make permanent preparations of the injected lymphatics, the blue 

 should be mixed ^\ith half its volume of the blue gelatin mass (§ 1450, Frey, A). 



For the structure of the lymphatic vessels, see § 984. 



Preparation— Fig. 103.— A cat was fed as described above 

 (§ 985 ). Then the arteries, but not the veins, were injected, and the 

 abdomen and thorax were opened as there described. The position 

 of the large lacteal trunk crossing the Y. mesenterica superior was 

 then found as described, and a V-shaped incision made in it with 



