CHAPTER II. 



INTERPRETATION OF APPEARANCES. 



APPARATUS AND MATERIAL FOR CHAPTER II. 



A laboratory, compound microscope (§ 74) ; Preparation of fly's wing (see ap- 

 pendix) ; 50 per cent, glycerin ; Slides and covers ; Preparation of letters in 

 stairs (Fig. 23 in PI. Ill) ; Mucilage for air-bubbles and olive or clove oil for oil- 

 globules (g Si) ; Solid glass rod, and glass tube (§ 89) ; Collodion fj 91) ; Carmine, 

 India ink, or lamp black (§ 93) ; Frog, and castor oil or paraffin, micro-polari- 

 scope (§95). 



INTERPRETATION OF APPEARANCES UNDER THE MICROSCOPE. 



§ 75. 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 ob- 

 jects 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 in- 

 crease in magnification 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 undertakes 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 appearances being quite differently interpreted 

 by eminent observers- 



§ 76. Dust or Cloudiness on the Ocular.— Employ the iS mm. 

 {% in.) objective, low ocular, and fly's wing, as object. ' 



Unscrew the field-lens and put some particles of lint or dark cloth on 

 its upper surface. Replace the field-lens and put the ocular in position 



