MAMMALIA— PHYSIOLOGY 455 



Aves. In the birds the renal portal system has almost completely disap- 



peared. The two renal portal veins formed by the division of the 

 caudal send off only a few branches to the kidneys, known as the 

 efferent renal veins, the main vein passing through the substance 

 of the kidney and joining the femoral vein from the leg to form the 

 iliac vein. The two iliacs unite to form the postcaval. 



Mammalia. There is no trace of a renal portal system in the mammalia. 



Blood. Functions of the Blood. — i. Carries food-stufFs to the 

 tissues. 



1. Carries oxygen to the tissues. 



3. Medium of transmission of the internal secretion of certain 

 glands. 



4. Removes waste products from the tissues and carries them to 

 the organs. 



5. Aids in equalizing the temperature and water content of the 

 body. 



Amount of Blood in Per Cent in Different Parts of the Body 



Spleen 0.23 per ce 



Spinal cord and Brain 1.24 pe/cent 



Kidney 1.63 nfer cent 



Skin 2.10 ier cent 



Intestines 6.30 peTiBent 



Bones 8.24 per oent 



Heart, Lungs and Blood vessels 22.76 peyxent 



Resting muscle 29.20 p/r cent 



Liver 29.30 |(gr cent 



Chemical Composition of the Blood. (Schmidt) 



Water 788.71 pe/cent 



Proteins and extractives 191.78 pM^xent 



Fibrin (from fibrinogen) 3.93 per cJnt 



Hematin (and iron) 7.70 pec/cent 



Salts 7.88 per cent 



1,000.00 peVsent 



Blood constitutes about 7 per cent by weight of the human body, 

 a man having about 5 liters of blood in his body. Its specific 

 gravity varies from 1,050 to 1,055 ^^ children and women, and from 

 1,057 to 1,062 in men. The specific gravity of the corpuscles is 

 about 1,105, and that of the plasma, about 1,030. The specific 

 gravity is generally in direct proportion to the hemoglobin percentage 



