THE FROG : HISTOLOGY, GERM CELLS, DEATH 99 



Blood is classed among the skeletal tissues on account 

 of the plentifulness of its fluid ground substance, although 

 it only acts as a supporting tissue when under high pressure 

 it renders an organ turgid. The fluid part of blood is 

 known as the plasma, the cells as blood corpuscles. They 

 are of two kinds, red and white. Each red corpuscle is a 

 thin, biconvex, oval disc, yellow in colour owing to the 



FlG. 58. — A portion of the bladder of a frog, stained and highly 

 magnified. 



c.t.c, Connective-tissue cell ; vi./., unstriped muscle fibres ; n.ej>., nuclei of the 

 epithelioid cells which cover and line the bladder. 



presence of a compound of a protein with an iron-contain- 

 ing organic substance. This compound is called hemoglobin, 

 and it has the power of uniting with oxygen to form a loose 

 compound known as oxyhcemoglobin, which is formed in 

 the respiratory organs and breaks down in the capillaries 

 of the tissues, yielding its oxygen. Thus it serves as a 

 carrier of oxygen. The same substance is found in the red 

 corpuscles of all backboned animals, but in man and other 

 mammals these corpuscles are round biconcave discs 



