MATERIAL WITHIN THE BODY 177 



145. The plasma. The plasma consists chiefly of water. In 

 it are dissolved various salts, organic substances derived from 

 the digested food, a little oxygen and carbon dioxid, and sub- 

 stances derived from various organs and tissues, some of them 

 waste products. Not every drop contains all these materials, or 

 all of them in the same proportion, for substances are constantly 

 coming into the blood and other substances are passing out. 



While passing through 

 certain organs the blood 

 takes up, in addition to 

 wastes, special chemical 

 products that have pecul- (^^ ^^~^ /^'^^ (^^\ 



iar effects upon the organs ^o sJ'^'^S b vKvi^V 



and activities of the body. " ^ ^y^^^" <_>- 



For example, fronri the thy- pig. 92. Human blood corpuscles . 

 Toid gland, a Y-shaped, 



spongy body Iving in front '\ ''"' more mmierous red corpuscles (about ^,L^ 



f fS 1 ' ' t ui ^ ^" diameter) in fiat and in edge view; 



01 the larynx, the blood b, the less numerous white or colorless corpuscles, 



absorbs a substance that ^"^ leucocytes (some barely larger than the red 



has an important influence °"''' °^^'''' T""'' ^^"''' ^' ^^?^^ *" '''^^"" ^"^ 



, , , m moving stage; note granulations and nuclei 



upon the development and 



workings of the brain. From the pancreas the blood absorbs a substance 

 that has an important influence upon the oxidation of sugars in the 

 cells. In recent times it has been possible to prepare extracts of this 

 substance (insulin) from the pancreas of other animals and to use it 

 in overcoming the condition known as diabetes, in which sugars are 

 insufficiently oxidized. 



From little bodies that lie next to the kidneys the blood absorbs two 

 or more substances that influence the muscles of the blood vessels and 

 that have some effect upon the nervous system. The amount of these 

 materials is increased whenever strong feelings are aroused, as fear or 

 anger ; and an increase of the amount in the blood causes the liver to 

 put out more glycogen, which becomes available as fuel in the active 

 organs. This seems to be the reason why a person can put out more 

 energy when excited. The adrenin, as this substance is called, also in- 

 terferes with the secretions and contractions of the stomach, so that di- 

 gestion cannot go on happily during anger (see page 153), and it hastens 

 the clotting of blood (see section 148). The products of a soft organ 

 lying in the front part of the chest in young mammals, the thymus, are 



