CHAPTER VII 

 THE FROG (continued) : THE MICROSCOPICAL EXAMINATION 



OF THE SIMPLE TISSUES 



BEFORE carrying our inquiries any further into the 

 anatomy and physiology of the frog it will be necessary 

 to devote some consideration to its microscopic structure 

 or histology, since there are many matters in connection 

 with the various organs which can be further elucidated 

 only by the examination of the minute structure of the 

 organs as revealed by the microscope (see p. 119). 



Let us, first of all, examine a drop of the frog's blood 

 under the low power of the microscope. It will at once 

 be seen that the blood is not a simple homogeneous 

 fluid, but that it contains a large number of minute solid 

 bodies floating in it. These are called by the general 

 name of blood-corpuscles : the fluid part of the blood in 

 which they float is called the plasma. At first, owing to 

 currents in the fluid, the corpuscles will be found to 

 move to and fro, but after a time they come to rest. 

 Under the high power you will notice that the corpuscles 

 are of two kinds. The greater number of them are 

 regularly oval in form (Fig. 26, C), and of a yellow colour. 

 If the drop of blood is thick enough in one part for the 

 corpuscles to lie over one another, so that the light 

 passes through two or three layers of them to reach the 



