GENERAL DIRECTIONS 23 



as some others. Under these requirements we may employ a 

 strong alcoholic solution of Bismarck brown which is actinically 

 opaque. By its use walls which are presented in section do not 

 transmit enough light to affect the plate even after rather long 

 exposures, while those walls which are presented in side view 

 and are relatively of little volume transmit enough light to make 

 a strong contrast. By using such process plates as the Imperial 

 a well-taken negative will show sharply contrasting black and 

 white and will bring out all the details. All of the photographs 

 in the present work were taken in this way. 



After staining the sections should be passed into oil of cloves 

 until thoroughly cleared, after which they should be mounted in 

 xylol balsam. 



