SUPPLEMENT. 377 



Some months ago I was engaged in teaching microscopy in 

 one of our public schools. At that time I had the class in 

 physiology in hand, and it was my especial purpose to show 

 them actually, structures which were described and pictured in 

 the text book used. I had not proceeded far before we ran 

 against this " Nasmyth's membrane," and I was compelled to 

 state substantially the experience which I have now related to 

 you. 



There is not a class of persons on earth less appreciated or 

 more poorly paid than those engaged in histological investiga- 

 tions, and for their indefatigable perseverance I entertain a 

 profound respect ; but it has often occurred to me that as a class 

 they have been content to work with very poor tools, and it is 

 safe to say that a great deal of the ground already studied will 

 have to be reinvestigated, and with better glasses with a bet- 

 ter knowledge of those manipulations requisite to the use of 

 wide-angled lenses. Nor can the necessary manipulations be 

 acquired in the ordinary routine of investigation ; it is an art 

 of itself, and calls for special attention, requiring as much 

 study as the art of manipulating a pianoforte or an organ. 



It is a very commonplace remark, that, for the purposes of the 

 histologist, low-angled glasses, of moderate definition, are the 

 best suited. And yet, if we consult their latest works, we will 

 nnd structures described that call for the best lenses of the 

 widest angles. Take, for instance, the muscle sheaths, or the 

 -axis cylinders of the nerves described by Frey, in his last 

 edition. Coming down to commonplace things, I affirm that 

 the simple trachea of a bee cannot be studied with advantage 

 with other than lenses of the widest angles. 



There is perhaps no microscopic object more common than 

 these tracheaes. They are to be found mounted in the cabinet 

 of every microscopist, and we have all of us read about them 

 in the books ; we have examined them again and again, times 

 without number, with objectives ranging from the inch to 

 the l-5th, or perhaps to the l-10th. Now I ask you take a look 

 at them on my account, and if possible inform me how these 

 tracheal coils terminate : what is the structure at their very last 

 end? What is the least diameter of these terminal coils ? Here 



