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 



- from the fluid. This is seen when an effervescing 

 liquid is agitated ; so that the movements of the blood and 

 <>f the tracheae 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 

 1 y 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 th.it 

 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, 9 heat units per hour ; which is 

 equivalent to 3,807 units of work. If one-fifth of this appears 

 as external work, 18,000 (V 3*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 clay by man 

 at 4,000 units per gramme of his body weight. This results 

 from setting down 320,000,000 graminr-inctres as a day's work 

 fi.r a man weighing No 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 

 v <> kilos, it gives ,,',,, 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 .?$ of a gramme of oxygen 



