1883] 



MICROSCOPICAL JOURNAL. 



43 



of the bulb, expells a single drop, 

 while by blowing steadily for a mo- 

 ment, or rapidly working the bulb, a 

 dishful of the reagent is obtained. 



When the plug of cotton becomes 

 foul, which will not be for a long 

 time, even with Hematoxylin stain, it 

 may be replaced by a fresh one by 

 simply uncorking the lower end {d) of 

 the large tube, pulling out the old 

 plug with a pair of forceps and insert- 

 ing a fresh one. The cotton should 

 be but loosely packed to work easily. 

 If the contracted end of the delivery 

 tube becomes clogged through long 

 disuse, it may be freed with a pin or 

 fine wire, and the first dishful of the 

 reagent returned to the bottle, when 

 it will be found that the succeeding 

 dishful will be perfectly filtered. 



Troy, N. Y. 



Distortion Produced by Camera 

 Lucidiis.* 



A short time ago Mr. Grunow re- 

 quested me to examine one of his 

 new camera lucidasf with care,, and 

 for that purpose he very kindly 

 adapted one of his instruments to fit 

 the ocular of my stand. The results 

 of "my examination, and the compari- 

 son between the Grunow, and the 

 Zeiss "double prism " camera lucidas 

 are, in brief, as follows : — 



The Grunow form gives a clear 

 image projected on the paper entirely 

 free from the base of the microscope, 

 while in the Zeiss form, as is well 

 known, only a portion of the field of 

 view is available for drawing, — in the 

 case of my own microscope about one- 

 half. 



When the light upon both paper 

 and object is adjusted with the ut- 

 most care, the pencil-point seems to 

 be as clearly seen in one instrument 

 as in the other. Mr. Grunow claims 



* Remarks made before the New York Mi- 

 croscopical Society at the meeting of March 

 2fl, 18S3. 



t See this Journai,, Vol. iii, p. 201. 



some superiority in this respect for 

 his form of construction over all 

 others. On the other hand, greater 

 care in adjusting the strength of the 

 light on object and paper is neces- 

 sary with the Grunow than with the 

 Zeiss, and a relatively stronger light 

 may be thrown upon the object when 

 using the latter, which is a decided 

 advantage, as more detail can then 

 be seen while drawing. To explain 

 the reason for this, I will briefly al- 

 lude to the principles upon which the 

 two cameras are constructed. It will 

 be remembered from the published de- 

 scription of the Grunow instrument,* 

 that in this form the light from the 

 object passes through two prisms 

 with their faces together, forming a 

 block of glass with parallel sides. 

 The object is seen, therefore, with an 

 intensity of illumination which cannot 

 be varied except by moving the mir- 

 ror. In drawing with a camera lu- 

 cida, some parts of an object can be 

 distinctly seen and readily followed 

 with a pencil, while other parts, being 

 either too delicate to be seen dis- 

 tinctly, or too black to allow the pen- 

 cil-point to be followed over them, 

 can only be perfectly drawn by chang- 

 ing the relative illumination of object 

 and paper. To some extent it is pos- 

 sible to do this with the Grunow in- 

 strument by means of the mirror. 



In the Zeiss instrument no glass 

 intervenes between the eye and the 

 object. The prisms are only em- 

 ployed to give a view of the pencil 

 and paper. The edge of the prism 

 nearest the eye bisects the cone of 

 rays coming from the ocular, or rather 

 the pupil of the eye receives a portion 

 of its light from the object by looking 

 over the edge of the prism down the 

 tube, while another portion comes 

 from the paper and is reflected into 

 the eye by the prism. Consequently, 

 the relative brightness of the paper 

 and the object as seen, can be varied 

 within certain limits by moving the 

 eye over the edge of the prism so as 



* Loc. cit. 



