THE BLOOD 25 



Composition of the Blood. To the naked eye the blood 

 appears as a thick but simple liquid ; but when examined 

 with a compound microscope, it is seen to be complex in 

 nature, consisting of at least two distinct portions. One of 

 these is a clear, transparent liquid ; while the other is made 

 up of many small, round bodies that float in the liquid. 

 The liquid portion of the blood is called the plasma ; the 

 small bodies are known as corpuscles. Two varieties of 



Poo 



FIG. 8. Blood corpuscles, highly magnified. A. Red corpuscles as they 

 appear in diluted blood. B. Arrangement of red corpuscles in rows between 

 which are white corpuscles, as may be seen in undiluted blood. C. Red cor- 

 puscles much enlarged to show the form. 



corpuscles are described the red corpuscles and the 

 white corpuscles (Fig. 8). Other round particles, smaller 

 than the corpuscles, may also be seen under favorable 

 conditions. These latter are known as blood platelets. 



Red Corpuscles. The red corpuscles are classed as 

 cells, although, as found in the blood of man and the 

 other mammals (Fig. 9), they have no nuclei. 1 Each one 

 consists of a little mass of protoplasm, called the stroma, 

 which contains a substance having a red color, known 

 as hemoglobin. The shape of the red corpuscle is that 

 of a circular disk with concave sides. It has a width of 

 about of an mch (7-9 m i crons2 ) and a thickness of 



1 In birds, reptiles, amphibians, and fishes the red corpuscles have nuclei (Fig. 9). 



2 The micron is the unit of microscopical measurements. It is equal to uW OJ 

 a millimeter and is indicated by the symbol M. 



