THE MICROSCOPE 339 



stances by which we are surrounded, should be studied as a 

 preliminary to any special line of microscopical investigation. 



16. The Study of Human Tissues. When this has been done 

 and familiarity with the use of the instrument has been ob- 

 tained, proceed to the study of the human body, for human 

 physiology is our subject. If the end of the finger be .pricked 

 with a pin, a drop of blood may be procured for examination. 

 Place this on one of the glass slides, cover it with a thin piece 

 of glass, press down the cover so as to make a thin layer, and 

 then examine with the magnifying power just mentioned. Do 

 not add water, for that will cause the blood corpuscles to dis- 

 appear. If the drop of blood is placed under the microscope 

 at once after being drawn from the finger, most interesting 

 phenomena will be observed. The red corpuscles will be seen 

 to arrange themselves in rows, like piles of coin, while the 

 blood is coagulating. The spherical, white corpuscles will be 

 left out of the rows of red discs, and, if the highest power be 

 used, will be seen to change their shape constantly. 



17. If you scrape with a dull knife the inside of the cheek, 

 the flattened scales of "pavement epithelium," or of the 

 insensible covering which, analogous to the scarf-skin on the 

 outer surface of the body, lines the cavities of its interior, 

 may be readily studied. They have the appearance of trans- 

 parent tiles, each enclosing a round or oval body, called its 

 nucleus. Dandruff and the scrapings from the skin of the 

 body are composed of scales like those of the mouth, but they 

 differ somewhat in being hardened. by horny matter, and in 

 having a very faint central body or nucleus. 



18. The Tissues of the Inferior Animals. The warm-blooded 

 animals do not differ in the tissues or microscopic structures 

 that compose them, but only in the amount and arrangement 

 of these tissues. Milne-Edwards says these tissues "do not 

 differ much in different animals, but their mode of association 



16. Directions for examining a drop of blood ? 



17. Examination of the scales of the mouth ? Dandruff? 



18. In what, as respects the tissues, do the warm-blooded animals differ ? Statement 

 of Milne-Edwards ? 



