NEGATIVE MAKING 69 



whilst we are working with medium powers, 

 and my medical friends having assisted in pro- 

 ducing one from diseased tissue under a low 

 power (Fig. 7), I will now endeavor to photo- 

 graph a normal one, requiring considerably 

 greater amplification, as a further example. 

 The slide is labeled " Human voluntary mus- 

 cle injected." Under a magnification of 200 

 diameters or more the striations are beauti- 

 fully shown, but it is too great to display the 

 injected arteries in a very satisfactory manner. 

 We must make the best of the situation, how- 

 ever, as it is the striations of the muscular 

 fiber we are after. The optical arrangement 

 comprises an |-inch of moderate angle by 

 Beck's; Ross' substage condenser, with me- 

 dium cone of light, and Spencer's aplanatic 

 ocular, i-inch. The radiant is acetylene, the 

 plate a Carbutt's slow ortliochromatic, with a 

 screen of yellow pot glass. An exposure of 

 three minutes is deemed necessary ; the devel- 

 oper is hydroquinon. A fine negative is the 

 result, reproduced in Fig. 10, magnified 200 

 diameters. All of the manipulations are the 

 same as those already described under low 

 power work. 



High Powers by Transmitted Light. For this 

 class of work but little changes are required 



