194 DETAILED SYNTHESIS. 



207. THE NECESSITY FOR WATER IN INCREASED 

 QUANTITY is SIGNIFIED by thirst, which very properly 

 exists when water passes away by the action of the 

 Skin to promote the loss of heat, but does not exist 

 when Water is removed by the Kidneys to increase 

 heat. 



208. BLOOD is a very complex fluid, composed large- 

 ly of Water, in which, as a vehicle, digested food, oxy- 

 gen from the air, and effete material from the tissues are 

 dissolved. 



209. BLOOD HAS THEREFORE a double character : it 

 is composed of useful and useless material. 



210. BLOOD OBTAINS FROM FOOD calorific material 

 in the form of fat and sugar, and nutritious material in 

 the form of liquid albuminose, with which is united the 

 necessary chemical compounds to supply the passive 

 tissues. 



211. BLOOD OBTAINS FROM DECOMPOSING TISSUE a 

 variety of compounds that are useless in the particular 

 tissue from which they are thrown off, yet may in part 

 be of use in some of lower grade, or may be burned, 

 producing heat, or else must be eliminated. 



212. THE BLOOD is THUS THE COMMON SOURCE of 

 materials of all the tissues and all the liquids, and is the 

 common receptacle of materials discarded by them ; yet 

 none of the substances composing the tissues exist in the 

 Blood in the same condition as in the tissues, nor do 

 most of the fluids. Some of the fluids are merely drawn 

 from the Blood. 



213. IN ADDITION, th<e Blood is composed in part of 

 an immense, almost incredible, number of Blood-cells. 

 In health there are nearly three thousand in every drop. 

 Less than seventeen hundred are never found, and some- 

 times twice that number : increase or diminution by any 

 great number indicates disease. 



-.- 7. HOW -? 208. What -? 209. What ? 210. What does -? 211. What 

 <loe t. ? 212. Of what - ? 218. Wlwt twiil - ? 



