38 AQUATIC MICROSCOPY FOR BEGINNERS. 



marvellous something that he had found in a cancer, 

 which turned out to be a magnified air-bubble. These 

 little air-drops often play an amusing 

 part at the beginning of the micros- 

 copist's career. In Fig. 4 are shown 

 several of different sizes. Let the 

 student examine a drop of saliva 

 or of soapsuds, and he will in 

 future be able to recognize the 

 ~ A- u vui troublesome things. Pictures or words 



Tig. 4.— Air-bubbles. = 



cannot convey so true an idea of 

 their appearance as a single sight of the bubbles them- 

 selves. At times they become entangled in the parts 

 of an object in such numbers as to interfere with its 

 examination. In these cases nothing can be done ex- 

 cept to lift the cover on the point of the needle, and 

 slowly lower it, or remove it entirely, add more water, 

 and reapply it carefully. In appearance the bubbles 

 are usually circular, with a broad black border which 

 varies in width and depth of color as the objective is 

 raised or lowered. Near the margin is a bright ring, 

 and in the center a bright' spot. They often float 

 about, and this movement adds much to the wonder 

 with which the novice usually regards them. 



If the student will have a note-book in which to jot 

 down his observations, or to keep a list of the objects 

 examined, it will not only aid him in forming habits of 

 accurate observation, but will be of great interest 

 when he has become an accomplished microscopist. 

 The entry may be simple, and may be made to serve 

 as a memorandum of items to refesh the memory. 

 Here is an example from a boy's note-book: "June 15, 

 1884 — Came across a pool .near the toll-gate with the 



