CIRCULATORY SYSTEM — PULSATIONS OF THE HEART. 
297 
conditions ; age, exercise and temperature, each contributing to con- 
trol its actions, while other less direct intlnences exert a subsidiary 
modifying effect. 
Injuries to the shell or to the animal have also a disturbing effect 
upon the activity of the heart, whose pulsations are greatly accelerated 
even by the careful removal of a piece of the shell, so that any 
attempt to ascertain the pulse rate in the thick-shelled species, by 
removing, however carefully, the shell covering the cardiac region, 
would only yield misleading results. 
Age, as in other animals, has a great influence on the rapidity of 
the heart’s pulsations. In man, according to Carpenter, the pulse 
decreases in rapidity from about 135 at birth to <S5 in youth and 72 
in adult life, and in the mollnsca there is the same change from the 
rapidly pulsating heart of the embryo to the comparatively deliberate 
contractions of the mature animal ; this being confirmed by Stiebel, 
who has recorded that in the embryo of Linuuva there are from 50 to 
70 pulsations per minute, which decrease to 30 as the animal advances 
in growth and eventually sink to 20 at maturity. The retarding 
influence of age is readily verified by comparing the rate of pulsations 
in immature and adult specimens of the same species under similar 
conditions ; thus an immature IlelLv cantiana showed 56 pulsations 
per minute, and a mature specimen of the same species 44 only ; 
a young Helu' kortensis showed 74 per minute, while a full-gTown 
individual was only 5.S per minute. 
Exercise has also, as in man and other animals, a most striking 
effect on the heart, varying according to the amount of exertion and 
other circumstances, the mere act of emerging from the shell almost 
instantly accelerating the pulse rate. A Iljjalinia cellaria, whose heart 
in repose beat 40 times per minute, immediately increased to 64 on 
the emergence of the animal from its shell ; Helix hortensis under 
similar circumstances showed a similar rapid augmentation from 58 
to 80, the acceleration in all cases being more abrupt at the muscular 
effort to commence movement than at the effort iieceG.sary to con- 
tinue it, thus the pulsations of a quiescent Helix fjrannhittt rose 
abruptly at the earliest movement from 46 to 54 per minute, after- 
wards gradually increasing to 58, 60 and 64 as the animal extended 
itself. 
Temperature is of pre-eminent importance in influenciug the 
action of the heart, although its effects have been overlooked by 
