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in a state of moderate activity and quietude, was about 82 or 83 a minute ; be- 

 fore the second moult 89, while before the third casting it had sunk down to 63 ; 

 and before its fourth to 45, while, before leaving its fourth stage, and before it 

 had ceased to feed, preparatory to pupating, the pulse was not more than 39. 

 "Thus the number gradually decreases during the growing larva state, but the 

 force of the circulation is very much augmented. Now when the insect is in a 

 state of perfect rest, previously to changing its skin, the number is pretty nearly 

 equal at each period, being about 30. When the insect has passed into the pupa 

 state it sinks down to 22, and subsequently to 10 or 12, and after that, during 

 the period of hibernation, it almost entirely ceases. But when the same insect 

 which we had watched from its earliest condition was developed into the perfect 

 state in May of the following spring, the number of pulsations, after the insect 

 had been for some time excited in flight around the room, amounted to from 110 

 to 139 ; and when the same insect was in a state of repose, to from 41 to 50. 

 When, however, the great business of life, the continuation of the species, has 

 been accomplished, or when the insect is exhausted, and perishing through 

 want of food or other causes, the number of pulsations gradually diminishes, 

 until the motions of the heart are almost imperceptible." Insects, then, he re- 

 marks, do not deviate from other animals in regard to their vital phenomena, 

 though it has been wrongly imagined that the nutrient and circulatory functions 

 are less active in the perfect than in the larval condition. 



The heart of a larval Gastrus eqni taken the day previous from a horse's 

 stomach beat from 40 to 44 times a minute (Scheiber) ; while Schroder van der 

 Kolk observed only 30 beats in the same kind of maggot. 



In the larva of Corethra, while at rest, the heart contracts from 12 to 16 or 18 

 times a minute, but when active the number rises to 22. The systole and dia- 

 stole last from 5 to 6 minutes. (Dogiel.) 



Temperature also affects the pulsations, as they increase in frequency with 

 a rise and decrease with a fall in temperature. 



Influence of electricity. The influence of electricity on the action of the 

 insect's heart, from Dogiel' s experiments, is such as to cause an acceleration in 

 the frequency of the beats, while an increase in the strength of the electric cur- 

 rents either diminishes the frequency of the beats or entirely stops the heart's 

 action. A violent excitation with the induction current causes a systole when 

 the heart's action has stopped for a long time ; and if the excitation lasts unin- 

 terruptedly, then the contractions after a while become noticeable, according to 

 the strength of the current. In such a case there are, however, interruptions 

 in the regularity, strength, and order of the contractions. (Kolbe.) 



Effects of poisons on the pulsations. Dogiel has also experimented on the 

 influence of poisons in the form of vapor or as liquid solutions on the pulsations 

 of insects, which is much as in vertebrates. The application of carbonic oxide 

 to the larva of Corethra, whose heart one minute previous to the poisoning beat 

 15 times a minute, accelerated the heart-beats in about 55 minutes to 25 pulsa- 

 tions in a minute. Afterwards there was a retardation in the pulse to the nor- 

 mal beat. Carbonic acid had a similar effect. 



The following results obtained by Dogiel are somewhat as tabulated by 

 Kolbe : - 



I. Substances which cause the pulsations of the heart to accelerate. 



a. An induction current of electricity, d. Oxalic acid, acting feebly. 



acting feebly. e. Carbolic acid, acting feebly. 



b. Ammonia, acting feebly. /. Potassium nitrate, acting feebly. 



c. Ethyl ether, acting feebly. g. Aconite, acting feebly. 



