384 HOW TO SEE WITH THE MICROSCOPE. 



almost, of contempt. They are too often regarded by the hist- 

 ologist as a class of observers who use the microscope as a mere 

 plaything ; and the fact that the diatomists are not altogether 

 agreed as to the structure of some of their favorite shells, is. 

 often used as an argument to show the folly of studying the 

 diatomacese at all ! 



All 'this, my friends, is sheer sophistry. The study of the dia- 

 tomacese is as legitimate as that of any other branch of the 

 science of biology, and the labors of the diatomists have not 

 been for naught ; it is to them, and to their constant demands 

 on the optician, that we are indebted for the wonderful 

 improvements which have been made in object-glasses; and I am 

 bold enough to tell you that skillful diatomists can tell you a 

 much concerning the structure of a diatom, as can the patholo- 

 gistequally skilled inform you as to the structure of a blood 

 corpuscle ! 



But to the student, to those who desire to prepare themselves 

 for advanced work, the study of the diatomaceae cannot be neg- 

 lected. No line of practice has yet been discovered that will 

 teach the student the use and management of his tools, that 

 can at all compete with the superior claims of these minute 'org- 

 anisms. It is said that " adversity tries us and shows up our 

 best qualities." These little shells, too, will try the would-be- 

 manipulator, and, like the country judge, show up his worst 

 qualities. 



It was not my purpose to enter at all into the details concern- 

 ing the use of objectives ; but it will perhaps be well not to let 

 the opportunity pass without alluding to the fact that a wide- 

 angled glass requires totally different management, in some 

 respects, from those of narrow apertures. 



Those who have been accustomed to the use of the low angles 

 will, on a slight acquaintance with glasses possessing wide aper- 

 tures, almost invariably assert that the latter do not give as 

 good results, when worked by central, of centrally disposed 

 light, as they are accustomed to get from the former. A 

 moment or two devoted to the consideration of the situation, 

 will, I think, furnish the key thereto. 



When we use a narrow-angled objective, the oblique or lateral 



