Lymph also contains white corpuscles similar to those in the blood, 

 lymphocytes particularly predominating. 



The amount of lymph flowing from the thoracic duct in twenty- 

 four hours has been found in human patients to vary from 1,200 to 

 2,280 c.c. per day. In a dog of 10 kilos, the amount was 640 c.c. 

 We cannot take this as indicative of the normal flow, for the escape 

 of lymph through a wound is unrestrained by the conditions which 

 pertain in the closed body. 



The Processes concerned in the Formation of Lymph. Consider- 

 able divergence of opinion is manifested as to these ; a vast amount of 

 evidence has accumulated which is held to support the various views 

 entertained by different authorities. From such experimental data 

 one great fact emerges namely, that lymph flow is the concomitant 

 of tissue activity. For example 



1. When the liver is active, either as the result of an injection of 

 peptone or during the processes of digestion, there is an increased 

 flow of lymph from the liver. 



2. When the salivary gland is made to secrete by stimulation of 

 the chorda tympani nerve (see p. 374), there is a marked increase of 

 lymph flow from the gland. 



3. When the pancreas is made to secrete as the result of- an injec- 

 tion of secretin (see p. 397), there is similarly an increased flow of 

 lymph from that organ. 



4. From the resting limbs there is practically no flow of lymph; 

 activity gives rise to a well-marked flow. 



The two chief views held in regard to lymph formation are the 

 mechanical and the secretory. The mechanical view holds that lymph 

 transudes from the blood-capillaries as the result of the processes of 

 filtration and osmosis. A higher pressure is supposed to pertain in 

 the capillaries and cause filtration. According to the secretory view, 

 lymph is formed as the result of cell activity. The cells actively 

 draw water, etc., from the blood-capillaries into the tissue spaces 

 according to their functional needs. 



The experimental evidence in regard to filtration consists chiefly 

 of experiments in which a r'se of capillary pressure is induced as the 

 result of partial or total blocking of the venous circulation. This 

 does not occur under normal conditions. The result, also, is an in- 

 creased flow of lymph, which differs considerably in composition from 

 that flowing under normal circumstances. 



Such an experiment is the ligation of the veins of a limb, which 

 causes an increased flow of lymph poorer in solids than normal and 

 red-coloured, owing to the presence of red corpuscles. Ligation of 

 the portal vein ra'ses the pressure in the capillaries of the intestinal 

 area, and causes a marked increase of lymph. Occlusion of the inferior 

 vena cava above the diaphragm causes an increased flow of lymph 

 from the liver, due, according to this view, to the rise in pressure in 

 the liver capillaries. Similarly, occlusion of the aorta causes an in- 

 creased flow of lymph from the liver, the pressure in these circum- 

 stances in the inferior cava being slightly raised or remaining unaltered. 



