[1] _Letters by Eminent Persons_ (Aubrey's Lives), ii. 324.
[2] _Life and Continuation._
[3] Strafford's _Letters_, i. 474.
[4] Laud's _Works_, vi. 447.
[5] _Thomason Tracts_, Brit. Mus. E 164 (15).
[6] _Archaeologia Cantiana_, ii. 190.
[7] _Dict. of Nat. Biog._ sub "Digby." See also Robert Boyle's _Works_
(1744), v. 302.
DIGBY, KENELM HENRY (1800-1880), English writer, youngest son of William
Digby, dean of Clonfert, was born at Clonfert, Ireland, in 1800. He was
educated at Trinity College, Cambridge, and soon after taking his B.A.
degree there in 1819 became a Roman Catholic. He spent most of his life,
which was mainly devoted to literary pursuits, in London, where he died
on the 22nd of March 1880. Digby's reputation rests chiefly on his
earliest publication, _The Broadstone of Honour, or Rules for the
Gentlemen of England_ (1822), which contains an exhaustive survey of
medieval customs, full of quotations from varied sources. The work was
subsequently enlarged and issued (1826-1827) in four volumes entitled:
_Godefridus_, _Tancredus_, _Morus_ and _Orlandus_ (numerous
re-impressions, the best of which is the edition brought out by B.
Quaritch in five volumes, 1876-1877).
Among Digby's other works are: _Mores Catholici, or Ages of Faith_ (11
vols., London, 1831-1840); _Compitum; or the Meeting of the Ways at
the Catholic Church_ (7 vols., London, 1848-1854); _The Lovers' Seat,
Kathemerina; or Common Things in relation to Beauty, Virtue and Faith_
(2 vols., London, 1856). A complete list is given in J. Gillow's
_Bibliographical Dictionary of English Catholics_, ii. 81-83.
DIGENES ACRITAS, BASILIUS, Byzantine national hero, probably lived in
the 10th century. He is named Digenes (of double birth) as the son of a
Moslem father and a Christian mother; Acritas ([Greek: akra], frontier,
boundary), as one of the frontier guards of the empire, corresponding to
the Roman _milites limitanei_. The chief duty of these _acritae_
consisted in repelling Moslem inroads and the raids of the _apelatae_
(cattle-lifters), brigands who may be compared with the more modern
Klephts. The original Digenes epic is lost, but four poems are extant,
in which the different incidents of the legend have been worked up by
different hands. The first of these consists of about 4000 lines,
written in the so-called "political" metre, and was discovered in the
latter part of the 19th century, in a 16th-century MS., at Trebizond;
the other three MSS. were found at Grotta Ferrata, Andros and Oxford.
The poem, which has been compared with the _Chanson de Roland_ and the
_Romance of the Cid_, undoubtedly contains a kernel of fact, although it
cannot be regarded as in any sense an historical record. The scene of
action is laid in Cappadocia and the district of the Euphrates.
Editions of the Trebizond MS. by C. Sathas and E. Legrand in the
_Collection des monuments pour servir a l'etude de la langue
neohellenique_, new series, vi. (1875), and by S. Joannides
(Constantinople, 1887). See monographs by A. Luber (Salzburg, 1885)
and G. Wartenberg (Berlin, 1897). Full information will be found in C.
Krumbacher's _Geschichte der byzantinischen Litteratur_, p. 827 (2nd
ed., 1897); see also G. Schlumberger, _L'Epopee Byzantine a la fin du
dixieme siecle_ (1897).
DIGEST, a term used generally of any digested or carefully arranged
collection or compendium of written matter, but more particularly in law
of a compilation in condensed form of a body of law digested in a
systematical method; e.g. the Digest (_Digesta_) or Pandects ([Greek:
Pandektai]) of Justinian, a collection of extracts from the earlier
jurists compiled by order of the emperor Justinian. The word is also
given to the compilations of the main points (marginal or hand-notes) of
decided cases, usually arranged in alphabetical and subject order, and
published under such titles as "Common Law Digest," "Annual Digest," &c.
DIGESTIVE ORGANS (PATHOLOGY). Several facts of importance have to be
borne in mind for a proper appreciation of the pathology of the organs
concerned in digestive processes (for the anatomy see ALIMENTARY CANAL
and allied articles). In the first place, more than all other systems,
the digestive comprises greater range of structure and exhibits wider
diversity of function within its domain. Each separate structure and
each different function presents special pathological signs and
symptoms. Again, the duties imposed upon the system have to be performed
notwithstanding constant variations in the work set them. The crude
articles of diet offered them vary immensely in nature, bulk and
utility, from which they must elaborate simple food-elements for
absorption, incorporate them after absorption into complex organic
substances properly designed to supply the constant needs of cellular
activity, of growth and repair, and fitly harmonized to fulfil the many
requirements of very divergent processes and functions. Any form of
unphysiological diet, each failure to cater for the wants of any special
tissue engaged in, or of any processes of, metabolism, carry with them
pathological signs. Perhaps in greater degree than elsewhere are the
individual sections of the digestive system dependent upon, and closely
correlated with, one another. The lungs can only yield oxygen to the
blood when the oxygen is uncombined; no compounds are of use. The
digestive organs have to deal with an enormous variety of compound
bodies, from which to obtain the elements necessary for protoplasmic
upkeep and activity. Morbid lesions of the respiratory and circulatory
systems are frequently capable of compensation through increased
activity elsewhere, and the symptoms they give rise to follow chiefly
along one line; diseases of the digestive organs are more liable to
occasion disorders elsewhere than to excite compensatory actions. The
digestive system includes every organ, function and process concerned
with the utilization of food-stuffs, from the moment of their entrance
into the mouth, their preparation in the canal, assimilation with the
tissues, their employment therein, up to their excretion or expulsion in
the form of waste. Each portion resembles a link of a continuous chain;
each link depends upon the integrity of the others, the weakening or
breaking of one straining or making impotent the chain as a whole.
The mucous membrane lining the alimentary tract is the part most subject
to pathological alterations, and in this connexion it should be
remembered that this membrane differs both in structure and functions
throughout the tract. Chiefly protective from the mouth to the cardia,
it is secretory and absorbent in the stomach and bowel; while the
glandular cells forming part of it secrete both acid and alkaline
fluids, several ferments or mucus. Over the dorsum of the tongue its
modified cells subserve the sense of taste. Without, connected with it
by the submucous connective tissue, is placed the muscular coat, and
externally over the greater portion of its length the peritoneal serous
membrane. All parts are supplied with blood-vessels, lymph-ducts and
nerves, the last belonging either to local or to central circuits.
Associated with the tract are the salivary glands, the liver and the
pancreas; while, in addition, lymphoid tissue is met with diffusely
scattered throughout the lining membranes in the tonsils, appendix,
solitary glands and Peyer's patches, and the mesenteric glands. The
functions of the various parts of the system in whose lesions we are
here interested are many in number, and can only be summarized here.
(For the physiology of digestion see NUTRITION.) Broadly, they maybe
given as: (1) Ingestion and swallowing of food, transmission of it
through the tract, and expulsion of the waste material; (2) secretion of
acids and alkalis for the performance of digestive processes, aided by
(3) elaboration and addition of complex bodies, termed enzymes or
ferments; (4) secretion of mucus; (5) protection of the body against
organismal infection, and against toxic products; (6) absorption of food
elements and reconstitution of them into complex substances fitted for
metabolic application; and (7) excretion of the waste products of
protoplasmic action. These functions may be altered by disease, singly
or in conjunction; it is rare, however, to find but one affected, while
an apparently identical disturbance of function may often arise from
totally different organic lesions. Another point of importance is seen
in the close interdependence which exists between the secretions of acid
and those of alkaline reaction. The difference in reaction seems to act
_mutatis mutandis_ as a stimulant in each instance.
_General Diseases._
Vascular lesions.
In all sections of the alimentary canal actively engaged in the
digestion of food, a well-marked local engorgement of the blood-vessels
supplying the walls occurs. The hyperaemia abates soon after completion
of the special duties of the individual sections. This normal condition
may be abnormally exaggerated by overstimulation from irritant poisons
introduced into the canal; from too rich, too copious or indigestible
articles of diet; or from too prolonged an experience of some unvaried
kind of food-stuff, especially if large quantities of it are necessary
for metabolic needs; entering into the first stage of inflammation,
acute hyperaemia. More important, because productive of less tractable
lesions, is passive congestion of the digestive organs. Whenever the
flow of blood into the right side of the heart is hindered, whether it
arise from disease of the heart itself, or of the lungs, or proceed from
obstruction in some part of the portal system, the damming-back of the
venous circulation speedily produces a more or less pronounced stasis of
the blood in the walls of the alimentary canal and in the associated
abdominal glands. The lack of a sufficiently vigorous flow of blood is
followed by deficient secretion of digestive agents from the glandular
elements involved, by decreased motility of the muscular coats of the
stomach and bowel, and lessened adaptability throughout for dealing with
even slight irregular demands on their powers. The mucous membrane of
the stomach and bowel, less able to withstand the effects of irritation,
even of a minor character, readily passes into a condition of chronic
catarrh, while it frequently is the seat of small abrasions,
haemorrhagic erosions, which may cause vomiting of blood and the
appearance of blood in the stools. Obstruction to the flow of blood from
the liver leads to dilatation of its blood-vessels, consequent pressure
upon the hepatic cells adjoining them, and their gradual loss of
function, or even atrophy and degeneration. In addition to the results
of such passive congestion exhibited by the stomach and bowel as noted
above, passive congestion of the liver is often accompanied by varicose
enlargement of the abdominal veins, in particular of those which
surround the lower end of the oesophagus, the lowest part of the rectum
and anus. In the latter position these dilated veins constitute what are
known as haemorrhoids or piles, internal or external as their site lies
within or outside the anal aperture.
Inflammatory lesions.
The mucous and serous membranes of the canal and the glandular elements
of the associated organs are the parts most subject to inflammatory
affections. Among the several sections of the digestive tract itself,
the oesophagus and jejunum are singularly exempt from inflammatory
processes; the fauces, stomach, caecum and appendix, ileum, mouth and
duodenum (including the opening of the common bile-duct), are more
commonly involved. _Stomatitis_, or inflammation of the mouth, has many
predisposing factors, but it has now been definitely determined that its
exciting cause is always some form of micro-organism. Any condition
favouring oral sepsis, as carious teeth, pyorrhoea alveolaris (a
discharge of pus due to inflamed granulations round carious teeth),
granulations beneath thick crusts of tartar, or an irritating tooth
plate, favours the growth of pyogenic organisms and hence of stomatitis.
Many varieties of this disease have been described, but all are forms of
"pyogenic" or "septic stomatitis." This in its mildest form is catarrhal
or erythematous, and is attended only by slight swelling tenderness and
salivation. In its next stage of acuteness it is known as "membranous,"
as a false membrane is produced somewhat resembling that due to
diphtheria, though caused by a staphylococcus only. A still more acute
form is "ulcerative," which may go on to the formation of an abscess
beneath the tongue. Scarlet fever usually gives rise to a slight
inflammation of the mouth followed by desquamation, but more rarely it
is accompanied by a most severe oedematous stomatitis with glossitis and
tonsillitis. Erysipelas on the face may infect the mouth, and an acute
stomatitis due to the diphtheria bacillus, Klebs-Loeffler bacillus, has
been described. A distinct and very dangerous form of stomatitis in
infants and young children is known as "aphthous stomatitis" or
"thrush." This is caused by the growth of _Oidium albicans_. It is
always preceded by a gastro-enteritis and dry mouth, and if this is not
attended to, soon attracts attention by the little white raised patches
surrounded by a dusky red zone scattered on tongue and cheeks.
Epidemics have occurred in hospitals and orphanages. Mouth breathing is
the cause of many ills. As a result of this, the mucous membrane of the
tongue, &c., becomes dry, micro-organisms multiply and the mouth becomes
foul. Also from disease of the nose, the upper jaw, palate and teeth do
not make proper progress in development. There is overgrowth of tonsils,
and adenoids, with resulting deafness, and the child's mental
development suffers. An ordinary "sore throat" usually signifies acute
catarrh of the fauces, and is of purely organismal origin, "catching
cold" being only a secondary and minor cause. In "relaxed throats" there
is a chronic catarrhal state of the lining membrane, with some passive
congestion. The tonsils are peculiarly liable to catarrhal attacks, as
might a priori be expected by reason of their Cerberus-like function
with regard to bacterial intruders. Still, acute attacks of tonsillitis
appear on good evidence to be more common among individuals predisposed
constitutionally to rheumatic manifestations. Cases of acute tonsillitis
may or may not go on to suppuration or quinsy; in all there is great
congestion of the glands, increased mucus secretion, and often secondary
involvement of the lymphatic glands of the neck. Repeated acute attacks
often lead to chronic inflammation, in which the glands are enlarged,
and often hypertrophied in the true sense of the term. The oesophagus is
the seat of inflammation but seldom. In infants and young children
thrush due to _Oidium albicans_ may spread from the mouth, and also a
diphtheritic inflammation spreads from the fauces into the oesophagus. A
catarrhal oesophagitis is rarely seen, but the commonest form is
traumatic, due to the swallowing of boiling water, corrosive or irritant
substances, &c. A non-malignant ulceration may result which later leads
on to an oesophageal stricture. The physical changes presented by the
coats of the stomach and the intestine, the subjects of catarrhal
attacks, closely resemble one another, but differ symptomatically. Acute
catarrh of the stomach is associated with intense hyperaemia of its
lining coats, with visible engorgement and swelling of the mucous
membrane, and an excessive secretion of mucus. The formation of active
gastric juice is arrested, digestion ceases, peristaltic movements are
sluggish or absent, unless so over-stimulated that they act in a
direction the reverse of the normal, and induce expulsion of the gastric
contents by vomiting. The gastric contents, in whatever degree of
dilution or concentration they may have been ingested, when ejected are
of porridge-thick consistency, and often but slightly digested. Such
conditions may succeed a severe alcoholic bout, be caused by irritant
substances taken in by the mouth or arise from fermentative processes in
the stomach contents themselves. Should the irritating material succeed
in passing from the stomach into the bowel, similar physical signs are
present; but as the quickest path offered for the expulsion of the
offending substances from the body is downwards, peristalsis is
increased, the flow of fluid from the intestinal glands is larger in
bulk, though of less potency as regards its normal actions, than in
health, and diarrhoea, with removal of the irritant, follows. As a
general rule, the more marked the involvement of the large bowel, the
severer and more fluid is the resultant diarrhoea. Inflammation of the
stomach may be due to mechanical injury, thermal or chemical irritants
or invasion by micro-organisms. Also all the symptoms of gastric catarrh
may be brought on by any acute emotion. The commonest mechanical injury
is that due to an excess of food, especially when following on a fast;
poisons act as irritants, and also the weevils of cheese and the larvae
of insects.
Inflammatory affections of the caecum and its attached appendix
vermiformis are very common, and give rise to several special symptoms
and signs. Acute inflammatory appendicitis appears to be increasing in
frequency, and is associated by many with the modern deterioration in
the teeth. Constipation certainly predisposes to it, and it appears to
be more prevalent among medical men, commercial travellers, or any
engaged in arduous callings, subjected to irregular meals, fatigue and
exposure. A foreign body is the exciting cause in many cases, though
less commonly so than was formerly imagined. The inflammation in the
appendix varies in intensity from a very slight catarrhal or simple
form to an ulcerative variety, and much more rarely to the acute
fulminating appendicitis in which necrosis of the appendix with abscess
formation occurs. It is always accompanied by more or less peritonitis,
which is protective in nature, shutting in the inflammatory process.
Very similar symptomatically is the condition termed perityphlitis,
doubtless in former days frequently due to the appendix, an acute or
chronic inflammation of the walls of the caecum often leading to abscess
formation outside the gut, with or without direct communication with the
canal. The colon is subject to three main forms of inflammation. In
simple _colitis_ the mucous membrane of the colon is intensely injected,
bright red in colour, and secreting a thick mucus, but there is no
accompanying ulceration. It is often found in association with some
constitutional disease, as Bright's disease, and also with cancer of the
bowel. But when it has no association with other trouble it is probably
bacterial in origin, the _Bacillus enteritidis spirogenes_ having been
isolated in many cases. The motions always contain large quantities of
mucus and more or less blood. A second very severe form of inflammation
of the colon is known as "membranous colitis," and this may be either
dyspeptic, or secondary to other diseases. In this trouble membranes are
passed _per anum_, accompanied by a pain so intense as often to cause
fainting. In severe cases complete tubular casts of the intestine have
been found. Often the motions contain very little faecal matter, but
consist only of membranes, mucus and a little blood. A third form is
that known as "ulcerative colitis." Any part of the large intestine may
be affected, and the ulceration shows no special distribution. In severe
cases the muscular coat is exposed, and perforation may ensue. The
number of ulcers varies from a few to many dozen, and in size from a pea
to a five-shilling piece. Like all chronic intestinal ulcers they show a
tendency to become transverse.
Chronic catarrhal affections of the stomach are very common, and often
follow upon repeated acute attacks. In them the connective tissue
increases at the expense of the glandular elements; the mucous membrane
becomes thickened and less active in function. Should the muscular coat
be involved, the elasticity and contractility of the organ suffer;
peristaltic movement is weakened; expulsion of the contents through the
pylorus hindered; and, aggravated by these effects, the condition
becomes worse, atonic dyspepsia in its most pronounced form results,
with or without dilatation. Chronic vascular congestion may occasion in
process of time similar signs and symptoms.
Duodenal catarrh is constantly associated with jaundice, indeed is most
probably the commonest cause of catarrhal jaundice; often it is
accompanied by catarrh of the common bile-duct. Chronic inflammation of
the small intestine gives rise to less prominent symptoms than in the
stomach. It generally arises from more than one cause; or rather
secondary causes rapidly become as important as the primary in its
incidence. Chronic congestion and prolonged irritation lead to deficient
secretion and sluggish peristalsis; these effects encourage intestinal
putrefaction and auto-intoxication; and these latter, in turn, increase
the local unrest.
Infective lesions.
The intestinal mucous membrane, the peritoneum and the mesenteric glands
are the chief sites of tubercular infection in the digestive organs.
Rarely met with in the gullet and stomach, and comparatively seldom in
the mouth and lips, tubercular inflammation of the small intestine and
peritoneum is common. Tubercular enteritis is a frequent accompaniment
of phthisis, but may occur apart from tubercle of other organs. Children
are especially subject to the primary form. Tubercular peritonitis often
is present also. The inflammatory process readily tends towards ulcer
formation, with haemorrhage and sometimes perforation. If in the large
bowel, the symptoms are usually less acute than those characterizing
tubercular inflammation of the small intestine. The appendix has been
found to be the seat of tubercular processes; in the rectum they form
the general cause of the fistulae and abscesses so commonly met with
here. Tubercular peritonitis may be primary or secondary, acute or
chronic; occasionally very acute cases are seen running a rapid course;
the majority are chronic in type. The tubercles spread over the surface
of the serous membrane, and if small and not very numerous may give rise
in chronic cases to few symptoms; if larger, and especially when they
involve and obstruct the lymph- and blood-vessels, ascites follows. It
is hardly possible that tubercular invasion of the mesenteric glands can
ever occur unaccompanied by peritoneal infection; but when the infection
of the glands constitutes the most prominent sign, the term _tabes
mesenterica_ is sometimes employed. Here the glands, enlarged, form a
doughy mass in the abdomen, leading to marked protrusion of the
abdominal walls, with wasting elsewhere and diarrhoea.
The liver is seldom attacked by tubercle, unless in cases of general
miliary tuberculosis. Now and then it contains large caseous tubercular
masses in its substance.
An important fact with regard to the tubercular processes in the
digestive organs lies in the ready response to treatment shown by many
cases of peritoneal or mesenteric invasion, particularly in the young.
The later sequelae of syphilis display a predilection for the rectum and
the liver, usually leading to the development of a stricture in the
former, to a diffuse hepatitis or the formation of gummata in the
second. In inherited syphilis the temporary teeth usually appear early,
are discoloured and soon crumble away. The permanent teeth may be sound
and healthy, but are often--especially the upper incisors--notched and
stunted, when they are known as "Hutchinson's teeth." As the result both
of syphilis and of tubercle, the tissues of the liver and bowel may
present a peculiar alteration; they become amyloid, or lardaceous, a
condition in which they appear "waxy," are coloured dark mahogany brown
with dilute iodine solutions, and show degenerative changes in the
connective tissue.
The _Bacillus typhosus_ discovered by Eberth is the causal agent of
typhoid fever, and has its chief seat of activity in the small
intestine, more especially in the lower half of the ileum. Attacking the
lymphoid follicles in the mucous membrane, it causes first inflammatory
enlargement, then necrosis and ulceration. The adjacent portions of the
mucous membrane show acute catarrhal changes. Diarrhoea, of a special
"pea-soup" type, may or may not be present; while haemorrhage from the
bowel, if ulcers have formed, is common. As the ulcers frequently extend
down to the peritoneal coat of the bowel, perforation of this membrane
and extravasation into the peritoneal cavity is easily induced by
irritants introduced into or elaborated in the bowel, acting physically
or by the excitation of hyper-peristalsis.
True Asiatic cholera is due to the comma-bacillus or spirillum of
cholera, which is found in the rice-water evacuations, in the contents
of the intestine after death, and in the mucous membrane of the
intestine just beneath the epithelium. It has not been found in the
blood. It produces an intense irritation of the bowel, seldom of the
stomach, without giving rise locally to any marked physical change; it
causes violent diarrhoea and copious discharges of "rice-water" stools,
consisting largely of serum swarming with the organism.
Dysentery gives rise to an inflammation of the large intestine and
sometimes of the lower part of the ileum, resulting in extensive
ulceration and accompanied by faecal discharges of mucus, muco-pus or
blood. In some forms a protozoan, the _Amoeba dysenteriae_, is found in
the stools--this is the amoebic dysentery; in other cases a bacillus,
_Bacillus dysenteriae_, is found--the bacillary dysentery.
Acute parotitis, or mumps, is an infectious disease of the parotid
glands, chiefly interesting because of the association between it and
the testes in males, inflammation of these glands occasionally following
or replacing the affection of the parotids. The causal agent is probably
organismal, but has as yet escaped detection.
New growths.
The relative frequency with which malignant growths occur in the
different organs of the digestive system may be gathered from the
tabular analysis, on p. 266, of 1768 cases recorded in the books of the
Edinburgh Royal Infirmary as having been treated in the medical and
surgical wards between the years 1892 and 1899 inclusive. Of these,
1263, or 71.44%, were males; 505, or 28.56%, females. (See Table I. p.
266.)
If the figures there given be classified upon broader lines, the results
are as given in Table II. p. 266, and speak for themselves.
The digestive organs are peculiarly subject to malignant disease, a
result of the incessant changes from passive to active conditions, and
vice versa, called for by repeated introduction of food; while the
comparative frequency with which different parts are attacked depends,
in part, upon the degree of irritation or changes of function imposed
upon them. Scirrhous, encephaloid and colloid forms of carcinoma occur.
In the stomach and oesophagus the scirrhous form is most common, the
soft encephaloid form coming next. The most common situation for
cancerous growth in the stomach is the pyloric region. Walsh out of 1300
cases found 60.8% near the pylorus, 11.4% over the lesser curvature, and
4.7% more or less over the whole organ. The small intestine is rarely
attacked by cancer; the large intestine frequently. The rectum, sigmoid
flexure, caecum and colon are affected, and in this order, the
cylindrical-celled form being the most common. Carcinoma of the
peritoneum is generally colloid in character, and is often secondary to
growths in other organs. Cancer of the liver follows cancer of the
stomach and rectum in frequency of occurrence, and is relatively more
common in females than males. Secondary invasion of the liver is a
frequent sequel to gastric cancer. The pancreas occasionally is the seat
of cancerous growth.
Sarcomata are not so often met with in the digestive organs. When
present, they generally involve the peritoneum or the mesenteric glands.
The liver is sometimes attacked, the stomach rarely.
Benign tumours are not of common occurrence in the digestive organs.
Simple growths of the salivary glands, cysts of the pancreas and
polypoid tumours of the rectum are the most frequent.
Animal parasites.
The intestinal canal is the habitat of the majority of animal parasites
found in man. Frequently their presence leads to no morbid symptoms,
local or general; nor are the symptoms, when they do arise, always
characteristic of the presence of parasites alone. Discovery of their
bodies, or of their eggs, in the stools is in most instances the only
satisfactory proof of their presence. The parasites found in the bowel
belong principally to two natural groups, Protozoa and Metazoa. The
great class of the Protozoa furnish amoebae, members of Sporozoa and
Infusoria. The amoebae are almost invariably found in the large
intestine; one species, indeed, is termed _Amoeba coli_. The frequently
observed relation between attacks of dysentery and the presence of
amoebae in the stools has led to the proposition that an _Amoeba
dysenterica_ exists, causing the disease--a theory supported by the
detection of amoebae in the contents of dysenteric abscesses of the
liver. No symptoms of injury to health appear to accompany the presence
of Sporozoa in the bowel, while the species of Infusoria found in it,
the _Cercomonas_, and _Trichomonas intestinalis_, and the _Balantidium
coli_, may or may not be guilty of prolonging conditions within the
bowel as have previously set up diarrhoea.
The Metazoa supply examples of intestinal parasites from the classes
Annuloida and Nematoidea. To the former class belong the various
tapeworms found in the small intestine of man. They, like other
intestinal parasites, are destitute of any power of active digestion,
simply absorbing the nutritious proceeds of the digestive processes of
their hosts. Nematode worms infest both the small and large intestine;
_Ascaris lumbricoides_, the common round worm, and the male _Oxyuris
vermicularis_ are found in the small bowel, the adult female _Oxyuris
vermicularis_ and the _Tricocephalus dispar_ in the large.
The eggs of the _Trichina spiralis_, when introduced with the food,
develop in the bowel into larval forms which invade the tissues of the
body, to find in the muscles congenial spots wherein to reach maturity.
Similarly, the eggs of the Echinococcus are hatched in the bowel, and
the embryos proceed to take up their abode in the tissues of the body,
developing into cysts capable of growth into mature worms after their
ingestion by dogs.
Vegetable parasites.
Numbers of bacterial forms habitually infest the alimentary canal. Many
of them are non-pathogenic; some develop pathogenic characters only
under provocation or when a suitable environment induces them to act in
such a manner; others may form the _materies morbi_ of special lesions,
or be casual visitors capable of originating disease if opportunity
occurs. Apart from those organisms associated with acute infective
diseases, disturbances of function and physical lesions may be the
result of abnormal bacterial activity in the canal; and these
disturbances may be both local and general. Many of the bacteria
commonly present produce putrefactive changes in the contents of the
tract by their metabolic processes. They render the medium they grow in
alkaline, produce different gases and elaborate more or less virulent
toxins. Other species set up an acid fermentation, seldom accompanied by
gas or toxin formation. The products of either class are inimical to the
free growth of members of the other. The species which produce acids are
more resistant to the action of acids. Thus, when the contents of the
stomach possess a normal or excessive proportion of free hydrochloric
acid, a much larger number of putrefactive and pathogenic organisms in
the food are destroyed or inhibited than of the bacteria of acid
fermentation. Diminished gastric acidity allows of the entry of a
greater number of putrefactive (and pathogenic) types, with, as a
consequence, increased facilities for their growth and activity, and the
appearance of intestinal derangements.