122 SCIENCE PRIMERS. [§ vil 



particles, mix fat, and broken meat, and empty wrap- 

 pings, and salts, and water, all together into a thick, 

 dirty, yellowish creamt Squeezed along the intestine 

 by the contraction of the muscular walls, the goodness 

 of this cream is little by little sucked up. The fat 

 goes drop by drop, particle by particle, into the 

 lacteals, and so away into the blood. The proteids, 

 anore and more dissolved the further they travel along 

 the canal, soak away into blood-vessel or into lacteal. 

 The salts and the water go the same way, until at 

 last the digested meat, with all its goodness gone, 

 with nothing left but indigestible wrappings, or perhaps 

 as well some broken bits of fibre or of fat, is cast 

 aside as no longer of any use. 



Thus all food-stuffs, not much altered, with 

 all their goodness unchanged, pass either at 

 once into the blood, or !irst into the lacteals 

 and then into the blood, and the useless 

 wrappings of the food-stuffs are cast away. 



While we are digesting, the blood is for ever rushing 

 along the branches of the aorta, through the small 

 arteries and capillaries of the stomach and intestine, 

 along the branches of the portal vein, and so through 

 the liver back to the heart ; and during .xie few seconds 

 it tarries in the intestine, it loads itself with food-stuffs 

 from the alimentary canal, becoming richer and richer 

 at every round. While we are digesting, the thoracic 

 duct is pouring, drop by drop, into the great veins of 

 the neck the rich milky fluid brought to it by the 

 lacteals from the intestine, and as the blood sweeps 

 by the opening of the thoracic duct on its way down 

 from the neck to the heart, it carries that rich milky fluid 

 with it, and the heart scatters it again all over the body. 



