28 PHYSIOLOGY FOR BEGINNERS CHAP. 



shape apparently of their own accord. This kind of move- 

 ment is called amoeboid, because it is well seen in a simple 

 organism called an Amoeba, met with in stagnant water. A 

 colourless corpuscle is a cell, the substance of which is different 

 from the stroma of a red corpuscle, and is often spoken of as 

 protoplasmic. In this protoplasmic cell-substance, which is 



FIG. 7. Changes of form of a colourless corpuscle in a few minutes. 



living material and consists chiefly of proteids, united with 

 water, salts, and certain other substances, are embedded a 

 number of granules, and generally nothing more is seen but a 

 small mass of granular or cloudy material. If water or very * 

 dilute acetic acid (vinegar) be added, the cell-substance be- 

 comes clear, and in it there is brought to view a rounded or 

 irregularly-shaped body, which is darker than the rest of the 

 cell. This body is called the nucleus. The nucleus is 

 brought to view because the acid has dissolved the granules 

 which were hiding it. The colourless corpuscles are then 

 nucleated cells, and this is the case in all animals. The red 

 corpuscles of man have no nucleus, and this is true of all the 

 higher animals, those that suckle their young ; but the red 

 corpuscles of birds, reptiles, and fishes have a large oval 

 nucleus. 



If a drop of the blood of a frog is examined with the 

 microscope the red corpuscles will be seen to be much larger than 

 those of man, and to be oval and biconvex and to have nuclei. 

 The white corpuscles of the frog are about the same size and 

 of the same structure as in man. 



Clotting of the Blood. Get a butcher to allow you to 

 catch the blood from an animal which he is killing into two 

 separate basins. Put one basin aside, and allow it to stand 

 undisturbed. Stir sharply the blood as it is flowing into the 

 other basin with a rough stick or bundle of twigs and keep on 

 stirring it for three or four minutes. When the blood in the 

 first basin is firmly set, which it will be in from fifteen to twenty 



