254 A TEXTBOOK OF PHYSIOLOGY 



the secretory view, that lymph and milk are formed by the special 

 activity of the gland cells. The cells of each organ draw what they 

 need from the blood. 



The fact that some bodies appear to be quickly transferred from 

 the tissue fluid to the venous blood, while others appear to be passed 

 on into the lymphatics, has led to the view that the bodies passed 

 into the lymphatics are toxic, and are taken to the lymphatic glands 

 to have this toxicity destroyed. It has been shown experimentally 

 that lymph injected into the arterial system causes marked effects 

 upon the arterial pressure and rate of heart-beat. 



The Movement of Lymph. To what factors is due the flow of 

 lymph ? In the amphibia and fishes there are special lymph hearts, 

 but these are lacking in mammals. The lymphatics have valves to 

 direct the flow, and these valves have special muscle fibres arranged 

 about them which, it has been suggested, act as a pumping mechanism. 

 Such a claim has not been substantiated. The vessels, however, 

 appear to be innervated with constrictor and dilator nerves, and it is 

 conceivable, although not proven, that alterations in the lumen 

 may aid the flow. 



According to the mechanical view, the flow of lymph is maintained 

 by the filtration pressure transmitted from the vis a tergo, the heart. 

 This point has already been debated. The heart-beat plays an im- 

 portant factor in pulsing organs full of blood, with each heart-beat. 

 This systolic filling squeezes on the lymph in the lymphatics. 



The chief factors in causing a flow of lymph are the activities of 

 the tissues, muscular movement, and the respiratory pump. 



The various serous membranes of the body are moistened by fluids 

 which more or less resemble lymph in composition. The amount 

 of protein in these different fluids varies considerably, although under 

 normal circumstances the quantity of such fluids is in some cases 

 so small that accurate analyses have not been made. The composi- 

 tion of the fluids is altered when there is increased formation due to 

 inflammatory disease, and it is such fluids which for the most part 

 have been analyzed. 



The per icar dial fluid is a somewhat sticky, lemon-coloured fluid, 

 which contains about 96-1 per cent, of water and 3-9 per cent, of solids. 

 The chief solids are proteins (2-8 per cent.) and salts, mostly sodium 

 chloride (0-7 per cent.). Traces of fat, lecithin, and cholesterin, are also 

 present. 







Pleural fluid is normally present in such small amounts that analyst 

 of the healthy fluid ha.s not been made. The same is true of normal 

 peritoneal fluid. 



The cerebro-spinal fluid is a thin, clear fluid, characterized by its 

 low specific gravity (1007 or 1008) and its low protein content. The 

 protein is of a globulin nature. A small amount of copper -reducing 

 substance is also present, which is probably sugar. In disease, the 

 constitution of the fluid may be altered in various ways. The state- 



