MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
559 
Duration of Life in different Media. 
An important subject connected with respiration is the capability which insects 
possess of supporting existence for a certain time in different media. It is a task of 
great difficulty to ascertain the precise length of time which different insects can con- 
tinue in noxious media without being destroyed. We are so little aware of all the 
circumstances which affect the respiration of insects, that it is almost impossible to 
ascertain the precise moment when they cease to respire, or become asphyxiated ; and 
it is still more difficult to be certain at what period, when respiration is suspended, 
life becomes extinct. We must therefore, in our experiments upon this subject, 
assume certain data, from which the comparative duration of life, under certain cir- 
cumstances, may be inferred. With this view I have assumed four data, which mark 
very distinct conditions of respiration. The first is that moment at which, when con- 
fined in the noxious medium, the insect, by the violence of its struggles and efforts 
to escape, begins to appear to respire with great difficulty, and is becoming asphyx- 
iated. The second is the moment at which it can no longer be observed to give signs 
of life by moving its limbs or the segments of its body, and when it may fairly be 
supposed that respiration is entirely suspended. The third is that moment at which, 
after being removed from the noxious medium, and exposed to the open air, the 
insect begins again to revive, its reviviscence being indicated by motions of its limbs 
or other parts of its body. The fourth is marked by the period when the insect is so 
far sufficiently recovered as to be again capable of locomotion. By comparing these 
circumstances in different insects, we obtain a comparative knowledge of the state of 
respiration as affected by different media. 
In the months of July and August 1832, I made a series of observations on different 
insects with these assumed data, and I then found that the order in which the vitality 
of insects appears to be affected in different media is as follows : hydrogen, water, 
carbonic acid, nitrous acid gas, chlorine, and cyanogen, as shown in the accompany- 
ing Table ; and I have since repeated the observations on several species of insects 
with similar results. 
