430 HEALTH AND DISEASE 



vessels and the minute muscles surrounding the lacteals in the villi. 

 The pressure under which the lymph moves is very low, and it is dis- 

 charged from the thoracic duct into that part of the blood vascular system 

 where the pressure is lowest, namely, into the veins just before their entry 

 into the right auricle of the heart. 



When the outward movement of the lymph towards this point is 

 impeded it accumulates in the vessels beyond the obstruction. This 

 condition is more marked, and appears earlier if the obstruction be of 

 such a nature as to affect the venous system as well as the lymphatic. 

 The conditions known as oedema and dropsy are then established. 



The composition of the lymph is very similar to that of the plasma 

 of the blood, but it contains more water and less proteid matter. In the 

 case of the horse there are about ninety-five to ninety-six per cent of 

 water, and four or five per cent of solids, of which about three parts are 

 albuminous or proteid substances, the remainder consisting of salts, the 

 most abundant of which is common salt or sodium chloride. 



The composition of chyle, consisting chiefly of the digested materials 

 contained in the alimentary canal, varies with the nature of the food 

 and the period of digestion at which it is examined. In the fasting 

 animal it does not diff'er materially from the lymph, but, with an oily 

 diet like milk, the proportion of fat undergoes great increase, and the 

 lacteals become conspicuous by their white colour. After passing through 

 the lymphatic glands, the lymph and chyle alike acquire the power of 

 coagulating or clotting, though in both instances the clot is feeble and 

 soft. 



6. THE ORGAI^S OF CIRCULATION 



THE BLOOD 



From the earliest ages the blood has been held to be one of the most 

 important constituents of the body, for it was natural, when death was 

 seen to follow alike in animals and in man the infliction of a small wound 

 (providing it opened a large vessel), to believe that as the blood drained 

 away, the life itself was leaving the body. The practice of strict Jews of 

 all periods of their history, acting up to the command: " But flesh, with the 

 life thereof, which is the blood thereof, shall ye not eat", is evidence of the 

 strong impress the constant association of loss of blood and of life has made 

 on the mind of man. In many points of view it is indeed the river of life, 

 for its flow supplies to all jDarts of the body the materials requisite for their 



