26 STUDIES IN PHYSIOLOGY 



known as blood plasma. Like the amoeba, these corpuscles 

 are single cells. Two kinds may be distinguished, which 

 from their color are known as red and white corpuscles. 



There are three hundred to seven hundred times as many 

 red corpuscles as white. But we shall consider the white 

 corpuscles first because of their similarity to the amoeba 

 both in structure and in activity. Each corpuscle consists 

 of a minute bit of protoplasm in which is imbedded a 

 nucleus. These blood cells have also the characteristic 

 amoeboid movement. By this method of locomotion they 

 can creep along in a direction opposite to that of the blood 

 current, and they have even been seen forcing their way 

 through the walls of small blood vessels by pushing out 

 false feet. They then wander about in the tissues of the 

 body and do us great service, as we shall see, especially in 

 time of disease. 



The red corpuscles have no power of independent motion. 

 They are circular disks, concave on both surfaces. 1 Some 

 idea of the minute size of these cells may be gained from the 

 fact that five millions of them are floating about in a drop 

 of blood the size of a pin head. There is no nucleus in the 

 red corpuscles; yet we consider them as modified animal 

 cells, since they are formed from cells having a nucleus. 



Cells in Other Tissues. If we examine microscopically 

 nerve tissue, muscle tissue, or any other building material of 

 animal bodies, we find each and all of them to be composed 

 of cells. These vary somewhat in size, although all are 

 microscopic. As we shall see there are characteristic forms 

 of cells for each tissue ; but every animal cell, so far as we 

 know, has a cell body and a nucleus. 



Intercellular Substance. When we look at the end of a 

 fresh soup bone, we see a white shining tissue, known as 



1 A good model of a red corpuscle can be made from clay or putty. 

 Roll a small mass about the size of the finger tip into a sphere, 

 flatten it until the thickness is one fifth the diameter ; then pinch the 

 flattened disk between the thumb and. finger. 



