166 A MANUAL OF PHYSIOLOGY 



of the circulating liquid may be almost doubled by the in- 

 jection of blood or normal saline solution without causing 

 death, and increased by 50 per cent, without any marked 

 increase in the pressure. The excess is promptly stowed 

 away in the dilated vessels, especially those of the splanchnic 

 area ; the water passes rapidly into the lymph, and is then 

 more gradually eliminated by the kidneys. 



From these facts we can deduce the practical lesson, 

 that blood-letting, unless copious, is useless as a means of 

 lowering the general arterial pressure, while it need not be 

 feared that transfusion of a considerable quantity of blood, 

 or of salt solution, in cases of severe haemorrhage will 

 dangerously increase the pressure. And from the physio- 

 logical point of view the term ' haemorrhage ' includes more 

 than it does in its ordinary sense. For as dirt to the 

 sanitarian is * matter in the wrong place,' haemorrhage to 

 the physiologist is blood in the wrong place. Not a drop of 

 blood may be lost from the body, and yet death may occur 

 from haemorrhage into the pleural or the abdominal cavity, 

 into the stomach or intestines. Not only so, but a man 

 may bleed to death into his own bloodvessels ; in shock, as 

 well as in ordinary fainting or syncope, the blood which 

 ought to be circulating through the brain, heart and lungs 

 may stagnate in the dilated vessels of the splanchnic area. 



The Lymphatic Circulation. As has already been mentioned, 

 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 are simply irregular spaces, more or less completely 

 lined with epithelioid cells, in the connective-tissue that everywhere 

 accompanies and supports the bloodvessels. The constituents of the 

 blood-plasma are filtered through, or, as some say, secreted by the 

 capillary walls into the lymph spaces, and there form the clear liquid 

 known as lymph, from which the cells of the tissues take up food, 

 and into which they discharge waste products. The lymph spaces 

 are connected with more regular lymphatic vessels, with lymphatic 

 glands at intervals on their course. These fall into 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 



