RESPIRATORY MOVEMENTS OF INSECTS. 
147 
motionless and insensible, and produced both respiratory motions, and movements of 
the legs and wings*. 
The dragon-fly is very susceptible of galvanism ; but if the wires be applied to the 
outer surface of the insect they produce little effect, because it is so bad a conductor. 
In all the experiments, therefore, from which I have drawn any conclusions, I first 
removed the head of the insect, and then, placing its under surface uppermost, passed 
a pin through the centre of the most anterior part of the thorax, and another through 
the last segment of the abdomen, and then fixed the insect to a table or flat piece of 
wood. I thus obtained a ready conduction for the galvanic current, when the heads 
of the pins were touched with the wires of the battery, and had the insect in a con- 
venient position for observing its movements. 
In regard to the influence of galvanism on the respiratory motions (to which alone, 
as in the former observations, I shall here refer), its almost constant effect is to accele- 
rate them. I have, by its influence, increased the respirations from thirty to 150 in 
the minute, but a less increase (e. g. from thirty to fifty) was more usual. Some- 
times, while galvanising in the method described above, I have observed an almost 
persistent respiratory contraction, so long as the current was continued ; and on 
breaking the current, the respiratory relaxations and contractions alternated as 
before. 
The effects of galvanism on the respiratory movements are well seen when the in- 
sect has been influenced by chloroform. For example, I exposed a recently caught 
dragon-fly to chloroform vapour. Soon, sensibility and all motions ceased, including 
the respiratory. I tried many plates of a trough excited first by water, and then by 
acid, but equally without effect ; but having waited till the respiratory movements 
were resumed, I again employed the same power, and excited the contractions as 
often as I chose, making them much more powerful than they were when not thus 
stimulated. 
The following chief conclusions may be drawn from the series of observations that 
have been related : — 
1. The respiratory movements of dragon-flies (and probably of other insects) are 
naturally subject to considerable and frequent variations in force and rate, the causes 
of many of these variations being as yet unknown. 
2. The respirations are always quickened by exercise, emotion, rise of temperature, 
galvanism, and mechanical irritation ; and the last three agents quicken them in the 
decapitated, as well as in the perfect insect. 
3. The respiratory movements of each segment of the trunk are, in some measure, 
* In these experiments the changes of temperature were produced by submersion in water ; but many others 
showed that submersion in water of the same temperature as the air produced no similar effects, and that those 
here described were equally produced in air of similarly varied temperature. 
