PHOTOGRAPHIC INTRODUCTION 9 



or twice during the process. This seems to keep 

 the bacilli clear and free from deposit. Should 

 development have been carried too far, the negative 

 may be cleared if it is worth keeping ; so, too, if the 

 light be not quite even, the thickened part may be 

 thinned by using the same clearing solution with a 

 brush. The cyanide and iodine reducer was usually 

 employed for this purpose. 



The tubes were all photographed with a 5-inch 

 Ross-Goertz anastigmatic lens, the reflections off the 

 sides of the glass being avoided by immersing the 

 tube in a water bath. Limelight was thrown on 

 the tube either from the front or back, occasionally 

 employing a ground glass between the illuminant and 

 the water bath. 



For all purposes " backed " plates were used. 



