IQi THE CIRCULATION OF TH BLOOD A\'D LYMPH 



vessels ; in surgical (also sometimes called traumatic or vascular) 

 shock, it would appear that the blood which ought to be circulating 

 through the brain, heart, and lungs may stagnate in the dilated veins. 

 The essential nature of ' vascular ' shock, which should be dis- 

 tinguished from the spinal shock described in Chapter XVI. is so 

 little understood, in spite of the large amount of work devoted to 

 the subject, that it would not be profitable to discuss it here. It may 

 be remarked, however, that there is no reason to suppose that ex- 

 haustion orlossof sensitiveness of the vaso-mo tor centre is concerned. 

 While an undue proportion of the blood is accumulated in the great 

 veins, the arterioles and capillaries of the splanchnic area, like those 

 of the skin, are contracted and contain less blood than normal (Lyon, 

 Janeway and Jackson, etc.). 



SECTION VII. THE LYMPHATIC CIRCULATION. 



As has already been stated, some of the constituents of the blood, 

 instead of passing back to the heart from the capillaries along the veins, 

 find their way by a much more tedious route along the lymphatics. 

 The blood capillaries are everywhere in very intimate relation with 

 lymph capillaries, which, completely lined with epithelioid cells, lie in 

 irregular spaces in the connective-tissue that everywhere accompanies 

 and supports the bloodvessels. The constituents of the blood-plasma 

 are filtered through, or secreted by the capillary walls into these lymph 

 spaces, and mingling there with waste products discharged by the cells 

 of the tissues, form the liquid known as tissue liquid or tissue lymph. 

 From the tissue liquid the lymph capillaries take up the constituents 

 of the ' lymphatic ' lymph, which then passes into larger lymphatic 

 vessels, with lymphatic glands at intervals on their course. These fall 

 into still larger trunks, and finally the greater part of the lymph reaches 

 the blood again by the thoracic duct, which opens into the venous 

 system at the junction of the left subclavian and internal jugular veins. 

 The lymph from the right side of the head and neck, the right extremity, 

 and the right side of the thorax, with its viscera, is collected by the 

 right lymphatic duct, which opens at the junction of the right sub- 

 clavian and internal jugular veins. The openings of both ducts are 

 guarded by semilunar valves, which prevent the reflux of blood from 

 the veins. Serous cavities like the pleural sacs, although differing 

 from ordinary lymph spaces, are connected through small opening', 

 called stomata, with lymphatic vessels. 



The rate of flow of the lymph in the thoracic duct is very small com- 

 pared with that of the blood in the arteries only about 4 mm. per 

 second, according to one observer. Nevertheless, a substance injected 

 into the blood can be detected in the lymph of the duct in four to seven 

 minutes (Tschirwinsky) . The factors which contribute to the main- 

 tenance of the lymph flow are : 



(1) The pressure under which it passes from the blood capillaries into 

 the lymph spaces and from the lymph spaces into the lymph capillaries. 

 The pressure in the thoracic duct of a horse may be as high as 12 mm. 

 of mercury; in the dog it may be less than i mm. The difference is 

 probably due, in part at least, to a difference in the experimental con- 

 ditions, dogs being usually anaesthetized for such measurements, horses 

 not. The pressure in the lymph capillaries must, of course, be higher 

 than in the thoracic duct how much higher we do not know. 



(2) The contraction of muscles increases the pressure of the lymph 

 by compressing the channels in which it is contained, and the valves 



