CIRCULATORY SYSTEM — PULSATIONS OF THE HEART. 
'29S 
must ivriters on malacological subjects, who have been usually 
content to cite the bare numerical result of a single observation, 
without noting the comlitions affecting the rajjidity of the pulsations. 
jMoqniu-Tamlon, in his admirable work on the Mollusca of France, 
records that the heart of Vitrlnn ])j/reinuc<( beats 44 times per minute 
and states that kSt. 8imon had noted So pulsations in ffeli.r fnsca, 
leading to the erroneous conclusion that the circulation of JfclLv is 
normally twice as active as that of IMr. Alder has also 
recorded that he counted 120 pulsations per minute in I'itriiM 
pel/iicidd, and this observation also conveys a wrong impression, as to 
obiserve so feverish a rate IMr. Alder iirobably held the shell between 
his lingers during examination, which also may have taken place in 
the sun or in a very warm room, as the heart of that species when 
resting in its usual haunts seldom exceeds 50 pulsations per minute, 
its oi)timum rate being probably between 50 and 40. 
Mo(|uin-Tandun has also recorded that the range of pulsations in 
(iastropods varies from 25 to S5 per minute, leading his readers to the 
wrong conclusion that the pulse never rises above the latter number 
nor falls below the lesser one. 
The striking effect of warmth in stimulating the heart’s action is 
readily seen by observing the pulsations of a suitalde species in its 
cool natural retreat and again after it has laid a minute upon the 
The vcriical lines connect llic corresponding points of temperature and pulse rate. 
'I'he vertical lines connect the corresponding points of temperature and pulse rate. 
Fi<;. .588. — T)iagram of the pulsations of the heart of Helix hoj-tensisy espcciallj’ illustrating the 
close correlation of its activity wiili the changes of tcmpcr.aiure and show ing the stimulating action 
of warmth and the inhibitory character of a decreasing temperature. 
palm of the hand, when the rajud change from a deliberate to a 
(piickly beating imlse will be plainly visible to the eye. Vitrina 
2 Klluckl(i, under such circumstances, may increase its heart’s pulsa- 
