374 THE TRACHEAL SYSTEM OF THE IMAGO. 
inammals, In man the amount of oxygen absorbed is less 
than sq'yoth of the body weight per hour. 
It must be observed, however, that in warm-blooded animals 
the proportionate amount of oxygen to the body weight in- 
creases very rapidly as the size of the animal experimented 
on diminishes ; thus in the Dormouse it equals ,4th of the 
body weight per hour, and in small birds it is even as much 
as y'gth, therefore it is clear that the comparison of the oxygen 
absorbed to the body weight of those warm-blooded vertebrates 
which approach most nearly to insects in size leads to a very 
different conclusion. 
On the other hand, insects absorb about twenty times as 
much oxygen as cold-blooded vertebrates—Frogs and Lizards 
—weight for weight, from I,000 to 2,000 times more than the 
higher Mollusca, and 200 to 400 times as much as the higher 
Crustacea, if the observations recorded by various observers 
are correct. 
The respiratory quotient, or the relation of the CO, given 
off to the O absorbed (S="75) is low; in man it is given 
2 
as o'9. This, perhaps, indicates that the proteid metabolism 
is more rapid, but it is capable of other interpretations, as, 
for example, that more hydrogen is oxidized in proportion to 
carbon; but our knowledge is too limited to justify any con- 
clusions on this point. 
As a single Cockchafer (Melolontha vulgaris) absorbs all the 
oxygen contained in seven cubic centimetres of air in an hour, 
the least quantity of air which must pass into the trachez in 
this time is 7 cc.=7,000 cubic millimetres, and that on the 
supposition that the whole of the oxygen contained in the in- 
spired air is absorbed. 
The spiracular sacs of the thorax are six in number, and I 
estimate their united cubic contents to be equal to about 6 
cubic millimetres. The spiracular sacs of the abdomen are 
twelve in number, and I do not think their united capacity ex- 
ceeds 2 cubic millimetres. The number of respiratory contrac- 
tions of the spiracular sacs may be estimated at about 120 per 
