108 NUTRITIONAL PHYSIOLOGY 



ally seen in the form of a disk slightly hollowed on its sur- 

 faces. It is about five times as wide as it is thick. A very 

 slight unbalanced pressure acting from one side will con- 

 vert it into a saucer- or even a cup-shaped form. It is re- 

 markably elastic, and springs back into its original shape 

 as soon as there is no longer a force acting to distort it. 

 Most cells of the body are variable in outline and in size, 

 but one red corpuscle is as much like another as though all 

 had been made in the same mold. The diameter does not 

 vary perceptibly from ^TTTT inch. This is the figure for 

 human blood; there is a standard size of corpuscle for each 

 animal species. 



The red corpuscles are often spoken of as cells, but their 

 claim to rank as such is questionable. Regarding them 



Fig. 15. Red blood-corpuscles. Several are shown in different 

 positions. The hollow centers are evident. In one case two cor- 

 puscles are overlapped to show that they are transparent. They 

 tend to run into piles, as shown at the right. A saucer-shaped form 

 is represented. 



from an anatomic standpoint, they lack a feature which is 

 reckoned an essential of the cell; namely, the nucleus. 

 On the physiologic side there is no good reason for suppos- 

 ing them to be alive. The fairest view, probably, is to 

 look upon each red corpuscle as a modified and, in a sense, 

 degenerate cell. A single substance has come to constitute 

 a very large percentage of its make-up. This is the 

 peculiar, iron-containing protein, hemoglobin. We shall 

 not be far wrong if we consider the corpuscle to be a packet 

 of hemoglobin moving passively at the mercy of the cur- 

 rent. Its function is clear and definite. Hemoglobin has 

 the property of combining with oxygen whenever the gas 

 is freely present in the surrounding medium. It has also 

 the property of releasing this oxygen when it comes into a 

 situation where there is a relative scarcity of the element. 



