CHAPTER III. 



INTERPRETATION OF APPEARANCES. 



APPARATUS AND MATERIAL FOR CHAPTER .III. 



A laboratory, compound microscope (§ 114) ; Preparation of fly's wing ; 50 per 

 cent, glycerin ; Slides and covers ; Preparation of letters in stairs (Fig. 86) ; Muci- 

 lage for air-bubbles and olive or clove oil for oil-globules ($ 127-130). Solid glass 

 rod, and glass tube (J 135-137) ; Collodion (ig 137) ; Carmine, India ink, or lamp 

 black (# 139-14 1 ) ; Frog, castor oil and micro-polariscope ($ 143). 



INTERPRETATION OF APPEARANCES UNDER THE MICROSCOPE. 



§ 120. General Remarks. — The experiments in this chapter are 

 given secondarily for drill in manipulation, but primarily so that the 

 student may not be led into error or puzzled by appearances which are 

 constantly met with in microscopical investigation. Any one can look 

 into a microscope, but it is quite another matter to interpret correctly 

 the meaning of the appearances seen. 



It is especially important to remember that the more of the relations 

 of any object are known, the truer is the comprehension of the object. 

 In microscopical investigation every object should be scrutinized from 

 all sides and under all conditions in which it is likely to occur in nature 

 and in microscopical investigation. It is best also to begin with objects 

 of considerable size whose character is well known, to look at them 

 carefully with the unaided eye so as to see them as wholes and in their 

 natural setting. Then a low power is used, and so on step by step until 

 the highest power available has been employed. One will in this way 

 see less and less of the object as a whole, but every increase in magnifi- 

 cation will give increased prominence to detail, detail which might be 

 meaningless when taken alone and independent of the object as a whole. 

 The pertinence of this advice will be appreciated when the student un- 

 dertakes to solve the problems of histology ; for even after all the years 

 of incessant labor spent in trying to make out the structure. of man and 

 the lower animals, many details are still in doubt, the same visual ap- 

 pearances being quite differently interpreted by eminent observers. 



Appearances which seem perfectly unmistakable with a low power 

 may be found erroneous or very inadequate, for details of structure that 

 were indistinguishable with the low power may become perfectly evi- 



