CHOICE OF OBJECTIVES FOR REGULAR WORK. 207 



favor and use. It is not a strictly necessary objective in 

 the laboratory, for the one-sixth will of course do all 

 that can be expected of the one-fourth, and a great deal 

 more besides. The one-fourth is used precisely under 

 the circumstances stated ; when there is work on hand 

 likely to call for the shifting of objectives, the one- 

 fourth is very likely to remain in its box. Thus it will 

 be seen that my " working '" battery of objectives is not 

 numerically very formidable, and I may add, not very 

 expensive. 



Having thus stated my own course in the way of se- 

 lecting objectives for my particular work, let us now 

 turn our attention to a condition of things which is 

 occurring everyday, to wit: A young physician just 

 graduated wishes to use the microscope in his (expected) 

 practice. It is important to him that the investment 

 in an outfit be made with reference to the strictest econ- 

 omy. The author has in the past, and is now, receiving 

 many letters of this sort, to one of which he replied 

 but a day or two ago substantially as follows: 



The fundamental idea in purchasing an outfit ought 

 to be this: To buy nothing with the view of replacing 

 it bye-and-bye for something better of the sort, with an 

 indefinite hope that the original article can be disposed 

 of at no great loss. On the contrary, let every purchase 

 be made and every detail carefully selected with the in- 

 tention of avoiding any future substitution or exchange. 

 Any departure from this fundamental law will be at the 

 sacrifice of strict economy ; therefore we reply to our 

 correspondent in" this tenor, recommending that he pur- 



