IIo NATURALISTS’ ASSISTANT. 
For scientific work “bristol board” and a “six H” lead 
pencil produce the best results. ‘The shades may be put in with 
India ink and a camel’s hair or, better, a sable brush. In 
case it be desired to color a drawing, water colors are best, 
and the moist water colors are the most convenient to use. 
It is frequently desirable to use certain colors for certain 
organs and thus through a series of drawings to indicate the 
parts with similar functions and the following list embraces 
the conventional colors most used. 
White or neutral tint, nerves. 
Red, heart and arteries. 
Blue, veins. 
Brown, the alimentary canal. 
Green, liver. 
Purple, renal organs. 
Yellow, female sexual organs. 
Orange, male sexual organs. 
In a series of drawings with these conventional tints the 
eye readily appreciates the principal features of the anatomy 
without the aid of descriptive text. Other organs than those 
enumerated may be left blank or colored according to the 
fancy of the artist. 
The various photographic processes of reproducing illus- 
trations have lately acquired great prominence and a few 
hints on preparing drawings for the photographer may prove 
of use. 
The “direct transfer’ process of the Heliotype Company 
is but poorly fitted for scientific work and the results are very 
