(x. H. F. Nuttall 
175 
(Swellengrebel, 1916, p. 23). The only observations not agreeing with 
the foregoing are those of Sikora (vm. 1915, p. 531),’who states that 
adults take 1-1|, at times 2-3, hours to feed, sucking intermittently. 
I have only observed such prolonged feeding in enfeebled lice, and 
agree with others that gorging usually lasts about 3-10' in hungry 
insects. When not ravenous they may feed for shorter periods. 
Digestive Processes. 
On examining the young unfed larva under a low power, the slight 
contents of the midgut present a greenish colour. When it gorges, 
its previously short flat body becomes elongated and swollen. Whilst 
feeding for the first time, it expels some of the ingested blood by the 
anus. This expulsion of undigested, bright red blood, takes place in 
all stages, when they feed to repletion; there is no evidence that it 
occurs when the insects feed moderately and at frequent intervals as 
they usually do under natural conditions. The issuing droplets of 
blood dry rapidly, and cohere to form short chains of irregular or spiral 
form and dark red colour, subsequently becoming blackish. Whilst 
the insect feeds, and for a variable period afterwards, the gut shows 
very active peristalsis. 
The rate at which digestion occurs is much influenced by temperature. 
After 4 days at 12° C., a larva will still appear swollen and red, whereas 
at 31-37° C. a reduction in volume takes place in a few hours, and the 
bright red colour soon vanishes, changing from the haemoglobin-red 
to reddish brown and black as digestion proceeds. Whereas the gorged 
midgut at first renders most of the internal organs invisible, it gradually 
contracts and appears as a blackish, median longitudinal line under a 
hand lens, and finally the excreta accumulate in the posterior reaches 
of the intestine, the various organs of the insect having become again 
visible by transparency. In the meantime the insect has voided a large 
amount of blackish excreta. When lice are kept at 28° C. they do not 
need to be fed as often as at 35-37° C. because they digest more slowly 
and lose less water. 
All who have studied lice have observed these appearances; Swam¬ 
merdam (ed. 1682, p. 60) observed the expulsion’of blood in the act of 
feeding; Sikora (vm. 1915, p. 532) noted that lice kept at 6-8° C. 
contained unaltered blood after 8-10 hours, whereas at 35° C. digestion 
was completed in that time; Widmann (18. vm. 1915, pp. 290-292; 
28. ix. 1915, pp. 1337-1338) found that the gut became empty in 10 
hours at 28-30° C., in 12 hours at 20° C., and in 16 hours at 15° C.; at 
