428 HEALTH AND DISEASE 



receptacle into which it is to be poured. During fasting the lacteals ouly 

 contain a clear fluid, and were on this account long overlooked. It is 

 only after the consumption of oily foods or of some such fluid as milk 

 that they present the white appearance which has led to the name of 

 lacteals (Latin lac, milk) being applied to them. 



Although the lacteals are highly important agents in the absorption 

 of the soluble constituents of the food, the part played by the blood- 

 vessels which ramify on the wall of the alimentary canal must not be 

 overlooked. In the lower Vertebrata, as in fishes, no lacteals exist, and 

 therefore all materials absorbed must be taken up through the walls of 

 the blood-vessels in these animals, while it is obvious that the presence of 

 a swift current of a thick fluid like blood on one side of the vascular wall 

 must constitute a favourable condition for the absorption of a thinner 

 and more difl"usible fluid from the other side. 



The Lymphatic System. — This system commences in the skin, 

 and in the little spaces between the elements of the tissues in almost all 

 parts of the body. It can be easily demonstrated by means of injections, 

 for if a needle with a fine bore be plunged into the skin or into the 

 muscles, and mercury or warm solution of gelatine holding some colouring 

 material in suspension, as vermilion or Prussian blue, be forced through 

 it with syringe, a beautiful and very close net-work of channels comes 

 into view, which is quite distinct from the blood - vessels, and has no 

 direct communication with them. The minuter blood - vessels, although 

 they come into very close relation with the cells of glands and the fibres 

 of muscle, do not actually touch them. There is always a layer of fluid, 

 named lymph, between the two, so that, separating the blood from the 

 actual constituents of every tissue, there are the wall of the blood-vessel 

 and the layer of lymph outside that wall, as well as the walls of the 

 vessels in which the lymph is contained, which indeed consists only of 

 very thin cells. It is in the irregular spaces that are thus formed that 

 the lymphatics arise. The spaces thus lined by flat cells soon, instead 

 of being irregular, become tubular. 



The Lymphatic Glands. — These bodies may be likened to oval 

 or rounded masses of sponge, into which the lacteals convey chyle and 

 the lymphatics lymph. 



Fig. 183 represents the structure of one of these glands. The gland 

 has an investing coat or capsule (7) which completely surrounds it. From 

 the capsule fibrous strands (6) pass into the gland, dividing it off like 

 partitions into spaces. The spaces round the circumference (or cortex) of 

 the gland are of considerable size, and are more or less oval (.3), while 

 the spaces towards the centre (or medulla) are irregular in shape, and 



