MATERIAL WITHIN THE BODY 



179 



Water 



CO« 



resulting from the breaking down of tissue cells, as well as live 

 cells that get into the blood from without, such as bacteria of 

 various kinds. 



2. As sensitive or irritable cells they may respond to a chemi- 

 cal stimulation, such as the presence of various kinds of poisons, 

 by producing substances capable of counteracting or neutral- 

 izing foreign chemicals. 



3. As moving cells they wander about from the lymph to the 

 blood, or vice versa, and even into the intestines. In this way 

 they carry with them 

 dead matter to be 

 thrown out, or they 

 crowd together in 

 large numbers and 

 produce special sub- 

 stances that counter- 

 act a local chemical 

 disturbance. 



Because of their 

 peculiar behavior in 

 the presence of for- 

 eign substances and 



Urea 

 L Y M P H 



Water 



Oxygen 



Sugar etc. 

 BLOOD 

 Protein etc. 



Salts 



L Y M P H 



Fig. 93. What goes through the wall of a capillary 



From the blood within the capillary, water, salts, 

 food, and oxygen pass out by osmosis; from the sur- 

 rounding lymph, carbon dioxid, urea, and water pass 

 into the blood. White corpuscles work their way 

 through the wall of the capillary, between the cells 



particles we have come to think of the white corpuscles as the 

 most important agents of keeping the body in health, at least 

 in relation to certain special diseases. 



White corpuscles are found in all animals that have blood, and they 

 are very much alike in all, so far as general appearance and behavior are 

 concerned. In our bodies the white corpuscles probably originate by the 

 division of ameba-like cells in the bone marrow and in certain enlarged 

 lymph spaces containing crowds of the white corpuscles. 



148. Clotting of blood. When blood is removed from a blood 

 vessel, whether it is taken out of the body or not, it usually be- 

 comes clotted, or thickened. This clotting is brought about by 

 the coagulation, or solidifying, of a certain protein in the plasma 

 known as fibrinogen, which means "iibrin-maker," since the 



