INFLUENCE OF THE MOVEMENTS OF RESPIRATION. 545 



purpose of collecting the fluid. 1 These observations were con- 

 firmed by Dal ton, who noted the interesting fact, that in ani- 

 mals poisoned with woorara, in which artificial respiration 

 was continued by insufflation, the phenomena were reversed ; 

 the abundant discharge then took place with insufflation, 

 when the parts contained in the thorax were compressed by 

 the distended lungs, and in the intervals, the flow became 

 scanty or ceased. 3 



The amount of influence exerted by the respiratory move- 

 ments upon the flow of the lymph and chyle can be best ap- 

 preciated by examining carefully the mechanism of its oper- 

 ation. 



With each act of inspiration, all the liquids, as well as 

 the air, are drawn toward the cavity of the thorax. In 

 this way, the thoracic duct is dilated and then becomes 

 most distended with fluid. At the same time, the flow of 

 lymph from the right lymphatic duct into the right subcla- 

 vian vein is increased. After the thoracic duct has been thus 

 dilated in inspiration, at the moment of expiration, in com- 

 mon with all the other parts contained within the thorax, it 

 undergoes compression ; the valves prevent the reflux of its 

 contents, and, as a necessary consequence, the fluid is then 

 discharged with increased force into 'the left subclavian. vein. 

 It can be readily understood how the act of inspiration, while 

 it has a tendency to fill the thoracic duct from below, op- 

 poses the discharge of fluid from a fistula. 



From all these considerations, it is evident that, although 

 there are many circumstances capable of modifying the 

 currents in the lymphatic system, the regular flow of the 

 lymph and chyle depends chiefly upon the vis a tergo / but 

 the vessels themselves sometimes undergo contraction, and 

 they are subject to occasional compression from surround- 

 ing parts, which, from the existence of numerous valves in 



1 COLIN, Traiie de Physiologic Comparee des Animaux Bomesiiques, Paris, 

 1856, tome ii., p. 90. 



2 DALTON, op. cit., p. 416. 



35 



