WHY DOES THE HEART BEAT 



299 



contraction is their {miction. 



In the developing embryo, these 

 rhythmically contracting cells grow 

 together, side b}' side, end by end, 

 forming elongated muscle fibres, which 

 placed layer upon layer, eventually 

 form the contractile ])ortion of the 



the organism and is adapted to changes 

 in the external environment. — The 

 American Museum Journal. 



Single muscle cell from heart of an eight-days-in- 

 cubated chicken. When a section of the heart tissue 

 is planted in the blood plasma and placed in an in- 

 cubator, cells like above grow out from it. isolate 

 themselves, and begin to contract rhythmically. 



cone-shaped heart. Together with this 

 growth there develop nerve terminals, 

 or ganglia, and nerve fibres which con- 

 nect the four-chambered heart with 

 the central nervous system. This is 

 essential for, although the heart is cap- 

 able of automatic rhythmic movement 

 due to the inherent property of the 

 muscle cells as we have already ex- 

 plained, it is extremely important that 

 this rhythmic contraction should prop- 

 erly serve the needs of its possessor. 

 It is necessary that some control should 

 be exerted over its activities, so that 

 when the beat becomes slow, it shotild 

 be accelerated, and when too rapid, it 

 should be inhibited. These results are 

 obtained by two sets of nerve fibres 

 coming from the central nervotts sys- 

 tem. One set carries diminishing, or 

 inhibiting, stimuli, the other augment- 

 ing, or accelerating, stimuli. Because 

 the rate of the heartbeat changes cjuick- 

 ly in response to variations of internal 

 and external conditions, these regula- 

 tory nerves are of the greatest value, 

 for throtigh their agency, the motor 

 power of the circulation is quickly ad- 

 justed to suit the changing needs of 



An Intelligent Snake. 



BY M. RUSSElvI. JAMES, CAUFORNIA. 



Some time ago one of your corres- 

 pondents made a plea for the common 

 garden snake, and drew attention to its 

 harmlessness and value. This Summer 

 we had an interesting illustration of 

 both the value and sagacity of these 

 pretty little reptiles. On one of the 

 motuitain roads, attention was attracted 

 to the C[ueer antics of a garter snake 

 that had been startled by the passers- 

 by, and was making frantic efforts to 

 get into a loose stone fence that extend- 

 ed along one side of the road. But it 

 seemed to be trying to get in tail first ! 

 On closer inspection it was discovered 

 that the snake was not "too scared to 

 know which end he was standing on" 

 but had good and sufficient reasons 

 for "turning tail." It had a strangle- 

 hold on a mucilaginous slug of a girth 

 greater than its own ; consequently a 

 forward entrance through the narrow 

 interstices of the stones was out of the 

 qtiestion and the snake was engineering 

 a backward pull. The interested spec- 

 tators remained quiet and watched the 

 pro Mig which was successfully ac- 

 co"" "d : the exploring tail hitting 



an opei ig between the stones and the 

 snake drawing itself and the slug back- 

 ward into its home qtiarters. 



Probably not many Eastern people 

 are acquainted with our Pacific coast 

 slugs. These are yellowish-brown 

 slimy creatttres that grow to prodigious 

 size in damp localities where the crop- 

 ping is good. They "sure-to-goodness" 

 cut a swath in gardens, mowing down 

 the succulent vegetation and leaving 

 behind them nothing but a trail of 

 white slime. As a check on these rav- 

 aging gastropods, this incident proves 

 the harmless garden snake to be a pub- 

 lic benefactor on the Pacific coast. — 

 Rural New Yorker. 



The geologists of Captain Scott's last 

 party found the seaweed movement of 

 the antarctic glaciers to vary from 

 about twenty feet for the ten coldest 

 months of the year to a yard a day dur- 

 insf mid-summer. 



