the formation of vegetable mould-第5节

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Bridgman；　and　we　have　seen　that　when　their　attention　is　engaged；　
they　neglect　impressions　to　which　they　would　otherwise　have　
attended；　and　attention　indicates　the　presence　of　a　mind　of　some　
kind。　　They　are　also　much　more　easily　excited　at　certain　times　than　
at　others。　　They　perform　a　few　actions　instinctively；　that　is；　all　
the　individuals；　including　the　young；　perform　such　actions　in　
nearly　the　same　fashion。　　This　is　shown　by　the　manner　in　which　the　
species　of　Perichaeta　eject　their　castings；　so　as　to　construct　
towers；　also　by　the　manner　in　which　the　burrows　of　the　common　
earth…worm　are　smoothly　lined　with　fine　earth　and　often　with　little　
stones；　and　the　mouths　of　their　burrows　with　leaves。　　One　of　their　
strongest　instincts　is　the　plugging　up　the　mouths　of　their　burrows　
with　various　objects；　and　very　young　worms　act　in　this　manner。　　But　
some　degree　of　intelligence　appears；　as　we　shall　see　in　the　next　
chapter；　to　be　exhibited　in　this　work；a　result　which　has　
surprised　me　more　than　anything　else　in　regard　to　worms。

Food　and　Digestion。Worms　are　omnivorous。　　They　swallow　an　
enormous　quantity　of　earth；　out　of　which　they　extract　any　
digestible　matter　which　it　may　contain；　but　to　this　subject　I　must　
recur。　　They　also　consume　a　large　number　of　half…decayed　leaves　of　
all　kinds；　excepting　a　few　which　have　an　unpleasant　taste　or　are　
too　tough　for　them；　likewise　petioles；　peduncles；　and　decayed　
flowers。　　But　they　will　also　consume　fresh　leaves；　as　I　have　found　
by　repeated　trials。　　According　to　Morren　｛18｝　they　will　eat　
particles　of　sugar　and　liquorice；　and　the　worms　which　I　kept　drew　
many　bits　of　dry　starch　into　their　burrows；　and　a　large　bit　had　its　
angles　well　rounded　by　the　fluid　poured　out　of　their　mouths。　　But　
as　they　often　drag　particles　of　soft　stone；　such　as　of　chalk；　into　
their　burrows；　I　feel　some　doubt　whether　the　starch　was　used　as　
food。　　Pieces　of　raw　and　roasted　meat　were　fixed　several　times　by　
long　pins　to　the　surface　of　the　soil　in　my　pots；　and　night　after　
night　the　worms　could　be　seen　tugging　at　them；　with　the　edges　of　
the　pieces　engulfed　in　their　mouths；　so　that　much　was　consumed。　　
Raw　fat　seems　to　be　preferred　even　to　raw　meat　or　to　any　other　
substance　which　was　given　them；　and　much　was　consumed。　　They　are　
cannibals；　for　the　two　halves　of　a　dead　worm　placed　in　two　of　the　
pots　were　dragged　into　the　burrows　and　gnawed；　but　as　far　as　I　
could　judge；　they　prefer　fresh　to　putrid　meat；　and　in　so　far　I　
differ　from　Hoffmeister。

Leon　Fredericq　states　｛19｝　that　the　digestive　fluid　of　worms　is　of　
the　same　nature　as　the　pancreatic　secretion　of　the　higher　animals；　
and　this　conclusion　agrees　perfectly　with　the　kinds　of　food　which　
worms　consume。　　Pancreatic　juice　emulsifies　fat；　and　we　have　just　
seen　how　greedily　worms　devour　fat；　it　dissolves　fibrin；　and　worms　
eat　raw　meat；　it　converts　starch　into　grape…sugar　with　wonderful　
rapidity；　and　we　shall　presently　show　that　the　digestive　fluid　of　
worms　acts　on　starch。　｛20｝　　But　they　live　chiefly　on　half…decayed　
leaves；　and　these　would　be　useless　to　them　unless　they　could　digest　
the　cellulose　forming　the　cell…walls；　for　it　is　well　known　that　all　
other　nutritious　substances　are　almost　completely　withdrawn　from　
leaves；　shortly　before　they　fall　off。　　It　has；　however；　now　been　
ascertained　that　some　forms　of　cellulose；　though　very　little　or　not　
at　all　attacked　by　the　gastric　secretion　of　the　higher　animals；　are　
acted　on　by　that　from　the　pancreas。　｛21｝

The　half…decayed　or　fresh　leaves　which　worms　intend　to　devour；　are　
dragged　into　the　mouths　of　their　burrows　to　a　depth　of　from　one　to　
three　inches；　and　are　then　moistened　with　a　secreted　fluid。　　It　has　
been　assumed　that　this　fluid　serves　to　hasten　their　decay；　but　a　
large　number　of　leaves　were　twice　pulled　out　of　the　burrows　of　
worms　and　kept　for　many　weeks　in　a　very　moist　atmosphere　under　a　
bell…glass　in　my　study；　and　the　parts　which　had　been　moistened　by　
the　worms　did　not　decay　more　quickly　in　any　plain　manner　than　the　
other　parts。　　When　fresh　leaves　were　given　in　the　evening　to　worms　
kept　in　confinement　and　examined　early　on　the　next　morning；　
therefore　not　many　hours　after　they　had　been　dragged　into　the　
burrows；　the　fluid　with　which　they　were　moistened；　when　tested　with　
neutral　litmus　paper；　showed　an　alkaline　reaction。　　This　was　
repeatedly　found　to　be　the　case　with　celery；　cabbage　and　turnip　
leaves。　　Parts　of　the　same　leaves　which　had　not　been　moistened　by　
the　worms；　were　pounded　with　a　few　drops　of　distilled　water；　and　
the　juice　thus　extracted　was　not　alkaline。　　Some　leaves；　however；　
which　had　been　drawn　into　burrows　out　of　doors；　at　an　unknown　
antecedent　period；　were　tried；　and　though　still　moist；　they　rarely　
exhibited　even　a　trace　of　alkaline　reaction。

The　fluid；　with　which　the　leaves　are　bathed；　acts　on　them　whilst　
they　are　fresh　or　nearly　fresh；　in　a　remarkable　manner；　for　it　
quickly　kills　and　discolours　them。　　Thus　the　ends　of　a　fresh　
carrot…leaf；　which　had　been　dragged　into　a　burrow；　were　found　after　
twelve　hours　of　a　dark　brown　tint。　　Leaves　of　celery；　turnip；　
maple；　elm；　lime；　thin　leaves　of　ivy；　and；　occasionally　those　of　
the　cabbage　were　similarly　acted　on。　　The　end　of　a　leaf　of　Triticum　
repens；　still　attached　to　a　growing　plant；　had　been　drawn　into　a　
burrow；　and　this　part　was　dark　brown　and　dead；　whilst　the　rest　of　
the　leaf　was　fresh　and　green。　　Several　leaves　of　lime　and　elm　
removed　from　burrows　out　of　doors　were　found　affected　in　different　
degrees。　　The　first　change　appears　to　be　that　the　veins　become　of　a　
dull　reddish…orange。　　The　cells　with　chlorophyll　next　lose　more　or　
less　completely　their　green　colour；　and　their　contents　finally　
become　brown。　　The　parts　thus　affected　often　appeared　almost　black　
by　reflected　light；　but　when　viewed　as　a　transparent　object　under　
the　microscope；　minute　specks　of　light　were　transmitted；　and　this　
was　not　the　case　with　the　unaffected　parts　of　the　same　leaves。　　
These　effects；　however；　merely　show　that　the　secreted　fluid　is　
highly　injurious　or　poisonous　to　leaves；　for　nearly　the　same　
effects　were　produced　in　from　one　to　two　days　on　various　kinds　of　
young　leaves；　not　only　by　artificial　pancreatic　fluid；　prepared　
with　or　without　thymol；　but　quickly　by　a　solution　of　thymol　by　
itself。　　On　one　occasion　leaves　of　Corylus　were　much　discoloured　by　
being　kept　for　eighteen　hours　in　pancreatic　fluid；　without　any　
thymol。　　With　young　and　tender　leaves　immersion　in　human　saliva　
during　rather　warm　weather；　acted　in　the　same　manner　as　the　
pancreatic　fluid；　but　not　so　quickly。　　The　leaves　in　all　these　
cases　often　became　infiltrated　with　the　fluid。

Large　leaves　from　an　ivy　plant　growing　on　a　wall　were　so　tough　that　
they　could　not　be　gnawed　by　worms；　but　after　four　days　they　were　
affected　in　a　peculiar　manner　by　the　secretion　poured　out　of　their　
mouths。　　The　upper　surfaces　of　the　leaves；　over　which　the　worms　had　
crawled；　as　was　shown　by　the　dirt　left　on　them；　were　marked　in　
sinuous　lines；　by　either　a　continuous　or　broken　chain　of　whitish　
and　often　star…shaped　dots；　about　2　mm。　in　diameter。　　The　
appearance　thus　presented　was　curiously　like　that　of　a　leaf；　into　
which　the　larva　of　some　minute　insect　had　burrowed。　　But　my　son　
Francis；　after　making　and　examining　sections；　could　nowhere　find　
that　the　cell…walls　had　been　broken　down　or　that　the　epidermis　had　
been　penetrated。　　When　the　section　passed　through　the　whitish　dots；　
the　grains　of　chlorophyll　were　seen　to　be　more　or　less　discoloured；　
and　some　of　the　palisade　and　mesophyll　cells　contained　nothing　but　
broken　down　granular　matter。　　These　effects　must　be　attributed　to　
the　transudation　of　the　secretion　through　the　epidermis　into　the　
cells。

The　secretion　with　which　worms　moisten　leaves　likewise　acts　on　the　
starch…granules　within　the　cells。　　My　son　examined　some　leaves　of　
the　ash　and　many　of　the　lime；　which　had　fallen　off　the　trees　and　
had　been　partly　dragged　into　worm…burrows。　　It　is　known　that　with　
fallen　leaves　the　starch…grains　are　preserved　in　the　guard…cells　of　
the　stomata。　　Now　in　several　cases　the　starch　had　partially　or　
wholly　disappeared　from　these　cells；　in　the　parts　which　had　been　
moistened　by　the　secretion；　while　it　was　still　well　preserved　in　
the　other　parts　of　the　same　leaves。　　Sometimes　the　starch　was　
dissolved　out　of　only　one　of　the　two　guard…cells。　　The　nucleus　in　
one　case　had　disappeared；　together　with　the　starch…granules。　　The　
mere　burying　of　lime…leaves　in　damp　earth　for　nine　days　did　not　
cause　the　destruction　of　the　starch…granules。　　On　the　other　hand；　
the　immersion　of　fresh　lime　and　cherry　leaves　for　eighteen　hours　in　
artificial　pancreatic　fluid；　led　to　the　dissolution　of　the　starch…
granules　in　the　guard…cells　as　well　as　in　the　other　cells。

From　the　secretion　with　which　the　leaves　are　moistened　being　
alkaline；　and　from　its　acting　both　on　the　starch…granules　and　on　
the　protoplasmic　contents　of　the　cells；　we　may　infer　that　it　
resembles　in　nature　not　saliva；　｛22｝　but　pancreatic　secretion；　and　
we　know　from　Fredericq　that　a　secretion　of　this　kind　is　found　in　
the　intestines　of　worms。　　As　the