(t. H. F. Nuttall 
203 
the sateen was wound smoothly around the rods and fixed in place with pins. 
The apparatus was placed in the shade of a low wall so that only bright diffuse 
light fell vertically into the funnel from the sky. 
1. Light and Shade. To determine if lice seek the shade under vertical 
illumination, the cell was carpetted white, and half of it shaded by a black 
cover. 
2. Black and White. To determine if lice prefer a black to a white back¬ 
ground, a circular piece of white linen, with two quarters blacked with India 
ink (Fig. 1 B) served as a carpet for the cell. 
3. Colours: Two methods were employed in testing the influence of 
colour 1 : (a) the cell was roofed by a transparent polychrome gelatin screen, 
being carpetted white, or (b) white light entered the cell from above, the 
carpet being polychrome. In both cases what appeared to my eye to be the 
colours of the spectrum were employed, the coloured areas being arranged 
radially (as shown in Fig. 1 A), a circular uncoloured surface, 5 cm. in diameter, 
being left in the centre. The dyes used for preparing the polychrome screen 
and carpet were the following: 
Violet 
Dye 
methyl violet 
Wave lengths transmitted through the screen- 
blue to w.l. 4900, and red beyond 6300 
Indigo 
toluidine blue 
indigo and blue to w.l. 4850 
Blue 
methylene blue 
indigo, blue and green to w.l. 5500 
Green 
lichtgriin 
blue and green from w.l. 4600 to 5750 
Yellow 
picric acid 
whole spectrum except blue (down to 4700) 
Orange 
orange G. 
green, yellow, orange and red below 5300 
Red 
trypanred 
yellow, orange and red below Na line 
The colour screen: seven tubes of ordinary 10 per cent, neutral nutrient 
gelatin, as used for bacteriological purposes, were warmed to melting point in 
a water-bath, and the requisite amount of each dye was added to each tube. 
A clean glass plate with lines of demarcation drawn thereon in melted paraffin, 
was placed on a levelling tripod, and each portion of coloured gelatin was 
poured over its apportioned area and spread with a glass rod. The paraffin 
lines set boundaries to the flow of the melted gelatin. After the gelatin had 
cooled and set, the glass plate was reversed over a shallow circular dish con¬ 
taining calcium chloride, whereby the gelatin became completely dried and 
presented the appearance of brilliantly stained glass. 
The coloured carpet: corresponding lines to those described above were 
drawn on a piece of linen by means of a brush charged with melted paraffin. 
1 An attempt was made to use the spectrum from an arc light in a dark room, 25 lice being 
confined in a glass cell measuring 3x2 inches the floor of which was covered with the colours 
projected by the prism. The insects showed a definite tendency to wander to the walls of the 
box at the red and violet ends, which, however, may have been due to the obliquity of the rays 
and the insects seeking darkness. Mr Mills (/. infra) very kindly placed the apparatus at my 
disposal. 
2 I am much indebted to Mr W. H. Mills, M.A., for determining these wave lengths for me from 
photographs of the spectra kindly taken by Mr Frederick Stoakley at the Chemical Laboratory, 
Cambridge. 
