TECHNICAL MICKOSCOPY. 



sight; it is, however, advisable not to work at the instrument 

 during the first hours of the morning, nor immediately after taking 

 food. If fatigue or irritation of the eyes is experienced, work 

 should be stopped for a few days. 



It is immaterial whether the inactive eye be closed or open 

 during observation. The observer should accustom himself to use 

 both eyes alternately ; they thus experience the same changes : 

 hence, on the supposition, of course, that they were originally 

 equal in strength, they will coincide both in power and distance of 

 vision through life; otherwise the active eye usually becomes 

 somewhat more short-sighted. The exclusive and continued use 

 of one eye is said, moreover, to produce a peculiar irritation of the 

 other. This is so far correct, that the eye which is usually in- 

 active receives a far brighter light-impression on looking through 

 the Microscope, and is more readily fatigued if we observe with it 

 for any length of time which obtains also with the healthy eye of 

 the beginner. As regards the smarting which long-protracted work 

 causes in the active eye, it is doubtful whether the alternate use of 

 both eyes does not produce just as great inconvenience as the 

 exclusive use of one eye. Many microscopists, however, have 

 habitually observed with the same eye during several years 

 without inconvenience. 



6. THE WORK-TABLE. 



The convenience of a well-arranged work-table, as to height, 

 size, &c., should not be under-estimated. It should be sufficiently 

 large and massive, and furnished with one or more drawers for the 

 various appliances, drawing prisms, glass vessels, &c. For dissec- 

 tions a slope let into the table is to be recommended, because 

 most bodies are seen more clearly upon a black ground. We must 

 pass over all other arrangements which may perhaps be serviceable 

 in this or in that case, but which may in general be dispensed 

 with. 



