CHAPTER XXIX. 



LYMPH FORMATION. 



Demonstration 5. A large dog is given a meal containing an 

 excess of fat (lard) several hours prior to the experiment. After 

 anaesthetising with morphine and ether and inserting tracheal and 

 carotid cannulae the thoracic duct is exposed as it enters the left 

 subclavian vein at the root of the neck. This operation is rather 

 difficult and should be performed as follows: after extending the 

 incision through skin and subcutaneous tissue down to the sternal 

 notch, the sterno mastoid and sterno hyoid muscles are cut as low 

 down as possible on the left side and reflected upwards. The ex- 

 ternal jugular vein is then followed downward till it joins the 

 subclavian, which is traced inwards to its union with the internal 

 jugular. In the fork at the union of these two veins the thoracic 

 duct is sought for by very careful dissection (see Fig. 65), great 

 care being exercised so as not to wound the pleura which lies 

 immediately beneath the vein. Just before entering the vein the 

 thoracic duct, curving forwards and outwards, is joined by the 

 somewhat smaller neck lymphatic. The duct is rendered visible 

 by the white creamy fluid it contains, the neck lymphatic being 

 similarly injected to a lesser degree. (Usually it is advisable to 

 ligate the neck lymphatic, but when possible a cannula should be 

 placed in it (pointing upwards) since the lymph flow from this 

 lymphatic does not behave exactly like that from the thoracic 

 duct). To introduce the cannula into the thoracic duct two liga- 

 tures are placed under the latter, the one next the subclavian vein 

 being tied, and a slit is made with a fine pointed sharp scissors in 

 the duct; the edge of the slit is then caught in a fine pair of forceps 

 and a glass cannula (with an outside diameter of about 1/32 inch) 

 inserted and tied in by the second ligature. If the creamy lymph 

 escapes so freely from the slit in the duct that it fills the wound 

 its flow should be controlled by pulling gently on the free ligature. 

 Usually a certain amount of lymph flow is desirable since it facili- 



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