166 THE BLOOD AND ITS CIRCULATION 



of toxin or poison, so the blood forms specific antibodies to fight 

 each kind of organism or its toxins. 



Blood Transfusion. — It has been found that there are four types 

 of human blood. One type includes about 50 per cent of all 

 people. After heavy losses of blood as in an accident or in an 

 operation, and in some illnesses, blood is injected into a vein of 

 the patient by transfusion from an artery of a volunteer. Before 

 this operation is performed, it is necessary to make a test to see if 

 the two persons have blood of the same type. This is done by 

 means of the agglutinin test : Red corpuscles of the person who is 

 to give the blood are added to the blood of the patient. If the red 

 corpuscles are agglutinated, then the bloods are of two different 

 types and transfusion cannot be made. Lysins may also be present 

 that dissolve foreign red corpuscles; hence they are called 

 hcBmoly' sins. Tests maj^ be made for these hsemolysins by adding 

 washed red corpuscles of the volunteer's blood to the serum of the 

 patient's blood. If the corpuscles are dissolved, this blood cannot 

 be used for transfusion. 



The Ductless or Endocrine Glands and their Secretions. - - In 

 addition to all the functions already mentioned, the blood has 

 another very wonderful work. We have already read about the 

 hormones (Gr. hormon, exciting), the chemical messengers or regu- 

 lators produced by the ductless or endocrine glands in various parts 

 of the body. The blood is the only means of communication be- 

 tween these glands and the tissues on which their hormones act. 

 Scientists are just beginning to understand the tremendous influ- 

 ence on life of some of these glands, among which are the thy'roid, 

 parathyroid, and thy'mus, small glands located in the neck; the 

 adre'nal and suprare'nal bodies, little glands, closely attached 

 to the kidneys ; the "pitu'itary body, at the base of the brain ; parts 

 of the pancreas; and parts of the egg-producing and sperm-produc- 

 ing organs, the o' varies and testes (tes'tez). 



The Thyroid. — It has been found, for example, that under- 

 secretion of the thyroid gland is responsible for the condition known 

 as cre'tinism, and that this condition can be cured by supplying 

 the patient mth th3T:"oid secretion, either by grafting a new thyroid 

 of another animal or by injecting or feeding with thyroid extract. 

 Overactivity of this gland produces exophthaVmic goiter, a condition 



