THE BACTERIOLOGICAL LABORATORY 23 



Another method for obtaining illustrations of 

 microscopic preparations is by means of the camera 

 lucida. Among the best of these instruments, 

 suitable for bacteriological purposes, are those of 

 Zeiss and Nachet. ' Combined with the use of a 

 micromillimetre objective, the camera lucida affords 

 also a simple method for the measurement of 

 bacteria.' 



The third and last method for obtaining illustra- 

 tions of microscopic preparations is drawing by 

 hand. If a white piece of card-board or smooth 

 drawing-paper is fixed at the same level as the stage 

 of the microscope ; by keeping both eyes open one 

 for looking at the object through the microscope, 

 and the other for looking at the piece of card-board 

 an image of the object is seen on the card, which 

 can be readily traced with a pencil. For drawing 

 bacteria, etc., no pencil is so well adapted as 

 Windsor and Newton's HHHH; the blacklead 

 being brought to its final point by gentle rubbing 

 on the surface of the finest ground glass, or, 

 better still, a very fine hone. For inking the pencil 

 drawings, the finest etching pens should be used 

 perhaps the best are those made by Joseph Gillott ; 

 and the same maker's No. 303 is also a very fine- 

 pointed pen. In addition to the pencils and pens 

 Indian-ink, water-colours, and brushes are neces- 

 sary. With practice and patience, very accurate 

 drawings of microscopic preparations can be made 

 by hand. 



Dissecting Instruments. For the dissection of 

 diseased organs, tissues, etc., certain instruments are 



