W. Nicoll 
167 
a purely vegetable diet were unsuitable for the development of the 
larvae and that a certain small proportion of animal matter was 
essential. On the other hand faeces derived from a purely meat diet 
are unsuitable on account of the rapidity with which putrefaction 
takes place. Again, in very watery motions there may be an 
insufficiency of food, but this must be exceptional. In certain laboratory 
cultures, moreover, obtained by repeated washing and sedimentation 
it may so happen that an insufficient amount of suitable food is left 
for the larvae and in consetjuence their growth will be retarded and 
possibly altogether arrested. 
This matter is of some importance in the experiments I am about 
to describe, as the cultures were usually obtained by the washing and 
sedimentation process. As, however, in every case controls were kept 
the results could be satisfactorily checked. 
A certain small supply of air is necessary for the development of 
the eggs and the growth of the larvae. When the larvae, however, 
are fully grown and ensheathed they can withstand deprivation of air 
for considerable periods. The air supply may be cut off in several 
ways, as for instance in a hermetically sealed vessel or a tightly stoppered 
bottle. Again the faecal material may be buried under a thick layer 
of earth or covered with a layer of water. Even the bulk of the faecal 
material itself, if compact enough, may prevent the ingress of air to 
the interior of the mass and so arrest the development of the more 
deeply situated eggs. 
The absence of air, however, though it arrests the development of 
the eggs, does not immediately kill them. They can survive for several 
days or even weeks, and if within that time they are supplied with air 
they may proceed to complete development. Looss has shown that in 
the absence of putrefaction and other deleterious conditions, the amount 
of air required for the complete development of the eggs and larvae 
may be quite small. 
With regard to temperature it has already been stated that the 
most favourable is between 65° and 85° F., the optimum probably 
being about 75° F. Within these limits, other conditions being favour¬ 
able, larvae generally reach their full development in 5-10 days. It is 
important, however, to know the absolute limits of temperature within 
which the eggs and larvae can survive and continue their development. 
Boycott determined the higher limit as 100° F. but at temperatures 
over 90° F. he found that the majority of the eggs and larvae died. 
Looss, however, found that eggs and larvae w'ould survive and develop 
