IQ5 HOW TO WORK 



Fibres of flax ; cotton; and silk of different colours, pi. XLIV, 



% 2 75- 

 Human hair, cat's hair, hair from blankets, fig. 275. 



The scales of butterflies and moths, particularly those of the 

 common clothes moth, pi. XLIV, figs. 273, 274. 



Fibres of wood swept from the floor, fig. 276, fragments of tea- 

 leaves, hairs from plants, vegetable cellular tissue, and spiral 

 vessels, pi. XXXVIII, fig. 242. 



Particles of sand. 



Many of these extraneous substances are figured in the plates 

 indicated, and I beg the student will not only carefully examine the 

 drawings, but place actual specimens of all objects .delineated under 

 his own microscope. 



In the examination of deposits from fluid we must bear in mind 

 the possibility of the introduction of a small quantity of one deposit 

 into another by the pipette used for examination, and in this simple 

 manner much difficulty and confusion may be caused to the micro- 

 scopist. The pipette should therefore be well washed immediately 

 after it has been used, and the water in which it is washed should be 

 very frequently changed. In taking fluids from different bottles and 

 other vessels the possibility .of introducing various substances must 

 be borne in mind. 



