384 THE TRACHEAL SYSTEM OF THE IMAGO. 
with a gas greatly facilitates its absorption, and when the 
tension is reduced, equally facilitates the escape of dissolved 
gas from the fluid. This is seen when an effervescing 
liquid is agitated; so that the movements of the blood and 
of the tracheze must assist in the transference of gases from 
higher to lower tensions. 
I shall now endeavour to show that there is still further, 
and I think indisputable evidence, that all the oxygen inspired 
by an insect is actually used in the metabolic processes of the 
body. 
Relation of the quantity of Oxygen consumed to the work done.— 
If it is assumed that the same quantity of oxygen absorbed 
liberates the same amount of actual energy in the insect and 
in the vertebrate, the external work capable of being performed 
by the insect will be either equal to or greater than that 
capable of being performed by the vertebrate, weight for weight, 
as the heat produced remains the same or becomes less. 
It is usually held that about } of the actual energy of 
oxidization is capable of appearing as external work in man. 
On the assumption that the relation of heat to work 
remains about the same as in the mammalia; as 7 cc. of air 
contain 0'002254 grammes of O, estimating the heat equivalent 
of one gramme of O at 4,000 centigrade units, 0°002254 grammes 
of O give, in round numbers, g heat units per hour; which is 
equivalent to 3,807 units of work. If one-fifth of this appears 
as external work, 18,000 (243,807) units per day will represent 
the external work capable of being done, in round numbers. 
I arrive at nearly the same result in another way, by 
estimating the work done in gramme-metres per day by man 
at 4,000 units per gramme of his body weight. This results 
from setting down 320,000,000 gramme-metres as a day’s work 
for a man weighing 80 kilos. The absorption of 800 grammes 
of oxygen per day is perhaps an under-estimate for this amount 
of work, but if it be taken and the weight of man estimated at 
80 kilos, it gives yb of a gramme of oxygen per day for each 
gramme of body weight. A Cockchafer weighing one gramme, 
taking in 7 cc. of air per hour, absorbs »'5 of a gramme of oxygen 
