Hardesty, spinal Nerves of the Frog. 105 



ment usually above that under which the photograph had been 

 made. 



After a short study of the section under the microscope, it 

 was found suprisingly easy to identify any fiber in a field of the 

 photograph with its original in the section. Thus, also, the 

 boundaries of the fields marked off on the photograph could be 

 readily determined in the microscope. 



The counting itself was largely mechanical. An automatic 

 registering machine, one common use of which is to count tel- 

 egraph poles, was modified by attaching to its finger press a 

 short steel rod. Into the end of this rod was inserted a needle 

 so arranged with a set screw that the point could be protruded 

 any distance required. Plate VII, Fig. 7, represents a photo- 

 graph of the machine as it was here employed. In want of a 

 better name it will be referred to as the " counter." When the 

 rod is pushed up, the counter with an audible "click" regis- 

 ters one ; the pressure removed, the rod springs back to its first 

 position. The machine registers up to 1000 and repeats. By 

 piercing with the needle the center of a fiber in the photograph, 

 the rod is pushed up and the counter records. Thus when 

 each fiber represented in a photograph has been punched, the 

 counter has recorded on its register the total number of fibers 

 in the section. When a section contained more than 1000 

 fibers, each thousand when indicated by the register, was noted 

 and the counting continued. Since the counter began to repeat 

 immediately upon reaching 1000, there was absolutely no dan- 

 ger of loss or mistake. 



Each field as marked off on the photograph was counted 

 separately. Not till all the fibers in one field had been counted, 

 was the counting of those in an adjacent field begun. The aid 

 of the microscope was most necessary in counting the small 

 fibers ; large blood vessels were distinguishable on the photo- 

 graph as well as in the microscope. Every case which occa- 

 sioned the least doubt was quickly and finally settled by an ap- 

 peal to the microscope. Sometimes, among the smaller fibers, 

 there appeared in the photograph what seemed to be two fibers 

 lying in such close contact as to resemble the figure 8. These 



