CH. XXIII.] FORMATION OF LYMPH 319 



continued pulsating after all the rest of the spinal cord and the brain were destroyed ; 

 while destruction of this portion, even though all other parts of the nervous centres 

 were uninjured, instantly arrested the hearts' movements. The posterior, or 

 ischiatic, pair of lymph-hearts were found to be governed, in like manner, by the 

 portion of the spinal cord corresponding to the eighth vertebra. Division of the 

 posterior spinal roots did not arrest the movements ; but division of the anterior 

 roots caused them to cease at once. 



Jnnervation of the Thoracic Duct. By determining the rate of outflow of a 

 fluid at constant pressure passing through the thoracic duct, Camus and Gley have 

 obtained evidence of the presence of nerves, causing both dilatation and constric- 

 tion of the duct. These are contained in the sympathetic chain below the first 

 thoracic ganglion. The effect of stimulation is principally dilatation. 



Relation of Lymph and Blood. 



The volume of blood in the body remains remarkably constant. 

 If the amount is increased by injection of fluids, at first its specific 

 gravity is lessened, but in a short time, often in a few minutes, it 

 returns to the normal. The excess of fluid is got rid of in two ways : 

 (1) by the kidneys, which secrete profusely ; and (2) by the tissues, 

 which become more watery in consequence. After the renal arteries 

 are ligatured, and the kidney is consequently thrown out of action, 

 the excess of water passes only into the tissues. 



On the other hand, a deficiency of blood (for instance, after 

 hemorrhage) is soon remedied by a transfer of water from the 

 tissues to the blood through the intermediation of the lymph. 



In severe haemorrhage life has often been saved by transfusion 

 of blood from another person. The transfer of the blood of another 

 animal to the human vascular system is usually dangerous, especi- 

 ally if the blood has been defibrinated, for the serum of one animal 

 is usually poisonous to another, producing various changes, of which 

 a breakdown of the corpuscles (haemolysis) is the most constant 

 sign. It is, however, quite unnecessary to use blood at all for this 

 purpose; saline (preferably Binger's) solution should be used 

 instead. 



Formation of Lymph. 



Carl Ludwig taught that the lymph flow is conditioned by two 

 factors: first, differences in the pressure of the blood in the capillaries 

 and of the fluid in the tissue spaces, giving rise to a, filtration of fluid 

 through the capillary walls; and secondly, chemical differences 

 between these two fluids, setting up osmotic interchanges through the 

 wall of the blood-vessel. (See further, next chapter.) 



If the lymph is produced by a simple act of filtration, then the 

 amount of lymph must rise and sink with the value of D d\ D 

 representing the capillary blood-pressure, and d the pressure in the 

 tissue spaces. 



In support of this mechanical theory, various workers in Ludwig's 



