Arthur Sheridan Lea Sir Michael Foster.

A text book of physiology online

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the sacral nerves produces contractions in the pregnant uterus;
it is stated that the mode of contraction is different in the two
cases, in the latter the longitudinally disposed fibres, in the
former the circularly disposed fibres being especially thrown
into action. Moreover, it is said that while the fibres passing
by the hypogastric nerve are vaso-constrictor towards the
uterine arteries, those passing by the sacral nerves are vaso-
dilator. Other observers have failed to obtain any such differ-
ence between circular and longitudinal contractions, and find
that in some animals at least, while contractions of the uterus
may be readily brought about by stimulation of the sympathetic
nerves from the lumbar region, passing through the hypogastric
nerves, contractions cannot with certainty be obtained by stim-
ulating the sacral nerves. On the other hand, stimulation of
the sacral nerves, of the second, third, and sometimes of the
first, readily produces movements of the vagina. It may be
added that stimulation of certain areas of the cerebral cortex
will give rise to movements of the uterus and of the vagina.

Digitized by


1142 PARTURITION. [Book nr.

§ 710. Though under normal circumstances efficient ut«rine
contractions do not set in until the full period of gestation is
completed, yet by reason of changes in the uterus or its con-
tents, occurring from natural causes or induced artificially, the
full swing of movements may, at almost any time, though at
some times more readily than at others, be brought about. On
the other hand it may be delayed for a considerable time beyond
the proper term. We may be said to be in the dark as to
why the uterus, after remaining for months subject only to
futile contractions, is suddenly thrown into powerful and effi-
cient action, and within it may be a few hours or even less gets
rid of the burden which it has borne with such tolerance for
so long a time. None of the various hypotheses which have
been put forward can be considered as satisfactory. There is
no evidence for the view, based on the occurrence of contrac-
tions in consequence of an asphyxiated condition of the blood,
that the onset of labour is caused by a gradual diminution of
oxygen or accumulation of carbonic acid in the blood, reaching
at last to a climax. Nor are there sufficient facts to connect
parturition with any condition of the ovary resembling that
accompanying menstruation. Nor can much stress be laid on
the supposition that the real exciting cause is the separation of
the decidua from the permanent uterine wall, the separation
being the outcome of the preceding processes of growth, since
the actual separation itself seems to be caused by the initial con-
tractions of labour, and the histological changes which precede
it are only one set of changes among many others all having
their goal in labour. We can only say that labour is the cul-
minating point of a series of events, and must come sooner or
later, though its immediate advent may at times be decided by
accident ; but it would not be profitable to discuss this question

The action of the abdominal muscles in parturition, at least
so much as takes place independently of the will, is, in contrast
to that of the uterine muscles, obviously a reflex act of a more
ordinary kind carried out by means of the spinal cord ; and we
may suppose that, though the mere contractions of the uterus
may serve as a possible source, the necessary stimulus is sup-
plied by the pressure of the foetus in the vagina ; in support of
this it may be noted that the action becomes much intensified
towards the end of labour as the stress and strain caused by the
advancing head tell more

§ 711. Hence as we
may with reason be consi
wholly a reflex or in a c
can readily be inhibited
central nervous system.
a hindrance to the progi

Digitized by



the entrance into the bedroom of a stranger often causes for a
time the sudden and absolute cessation of 'labour' pains, which
previously may have been even violent. Judging from the
analogy of micturition, we may suppose that this inhibition of
uterine contractions is brought about by an inhibition of the
centre in the lumbar cord leading to a sudden cessation of the
augmentor action of which we spoke above as far as the uterus
itself is concerned, and in a more direct way to a cessation of
the contractions of the abdominal muscles. Some observations
tend to shew that a region of the bulb exerts such an inhibitory
influence ; but the matter needs fuller investigation.

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§ 712. The child has at birth, on an average, rather less
than one-third the maximum length, and about one-twentieth
the maximum weight, to which in future years it will attain.

The composition of the body of the new-born babe, as com-
pared with that of the aHult, will be seen from the following
table, in which the details are more full than those given in
§ 413 ; the figures in brackets are more recent observations.

Weight of organ in percentage Weight of organ in
of Body-weight. adult, as compared

New-bom babe.

Adult babe taken as 1.

Eye -28
Brain 14-34 (12-28)
Kidneys -88
Skin 11-3

2-37 (2-25)



3-7 (3-34)

Liver 4-39 (5-03)
Heart -89 (-73)
Stomach and\ o co
Intestine / "^'^"^

2-77 (3.05)
-52 (-49)


13-6 (11-05)
15 (12-1)


Lungs 2-16
Skeleton 16-7



Muscles, &c. 2-34
Testicle -037




It will be obs<

to the whole bod

in the adult. Tl

feature, and has

physiological or
smaller body has
ally proportionati
portion is observe


Chap, hi.] THE PHASES OF LIFE. 1146

in weight twelve timesJ only between birth and full growth,
whereas the whole bocpr increases twenty times. The heart
and the liver according lo the newer observations behave very
similarly, and even according to the older observations lag con-
siderably behind the whole frame, whereas the lungs and the
alimentary canal almost exactly keep pace with it, and the
skeletal framework, in spite of its being specifically lighter in
its earlier cartilaginous condition, maintains throughout life
very nearly the same relative weight. The muscles on the
contrary grow more than twice as fast as the whole body ; the
great increase in these covers the relative decrease of the other
parts, and it is largely by the laying on of flesh and fat that
the babe gains the bulk of the man.

§ 713. We usually measure growth by taking account of
two sets of changes, changes of stature and changes of weight ;
and we may study both these changes in more than one way.

If we measure the height at intervals we may plot out the
curve of growth of stature , and when we do this we find that
the curve rises rapidly at first but afterwards more slowly,
shewing that the increment is decreasing, and at about the
twenty-fifth year ceases to rise at all. From thence to about
fifty years of age the height remains stationary, after which
there may be a decrease, especially in extreme old age. The
curve moreover is not regular, but indicates by its changes
that the increment of height in a given time is now smaller,
now OTeater.

The curve of weight is, on the whole, at first very similar
to that of height, rising in a somewhat similar way and shew-
ing similar irregularities; but instead of ceasing to rise at
about the twenty-fifth year it continues to rise, though marked
with many irregularities, and may continue to do so until about
the fortieth year. After the sixtieth year a decline of variable
extent is generally witnessed. It should be noted that in the
first few days of life, so far from there being an increase, there
is an actual decrease of weight, so that, even on the seventh
day the weight still continues to be less than at birth ; and a
similar post-natal loss of weight is observed in animals. If we
take the curve of growth from the impregnation of the ovum
onwards this post-natal loss of weight will appear as an abrupt
change in the curve due to the so to speak violent act of birth.
It should be added that the curves both of height and weight
exhibit differences dependent on sex, circiimstances, race, cli-
mate and the like.

We may also study the progress of growth by measuring
the increment of growth in a given time, in a year for instance,
and plotting out the curve of the yearly increment. When we
do this we obtain very instructive results. We find that the
yearly increment decreases very rapidly during the first two

Digitized by


1146 GROWTH. [Book iv.

or three years, then remains nearly stationary or even rises, and
at about the seventh or eighth year undergoes a marked fall.
This fall, however, is temporary only ; the curve soon rises
again and with some irregularities attains a maximum between
the twelfth and fifteenth year, from which point onwards it falls
rapidly with some minor irregularities. These marked varia-
tions in the increment of growth Avhich are obviously connected
with and preparatory to the important change which we call
puberty, are seen in the curves both of stature and of weight,
the changes in weight occurring however rather later than those
of stature, and both being somewhat different in boys from what
they are in girls. Both are also influenced by the conditions of
life; but a study of the curves of growth of young people living
under various surroundings, while it teaches the great impor-
tance of properly administering to the wants of youth, at the
same time illustrates the recuperative elasticity of the bodily
frame; it may often be observed that the ill effects of adverse
circumstances, provided they be not too great, are soon recov-
ered from under the influence of a happy change; food and
comfort will turn the abnormal fall in the curve of growth of a
starved waif into a sharp rise.

Lastly, we may study growth by observing the actual rate of
growth, by measuring the magnitude of the fraction of the total
weight which is added to the weight in a given time ; we take
weight because this is the most significant element of growth.
When this method is adopted, an examination of such statistics
as are available with regard to man, confirmed by the results of
careful observations on young animals, tends to shew that the
rate diminishes continually from birth onwards, the diminution
being rapid at first but slower afterwards, and being broken by
various irregularities. In other words, the power of growth
diminishes continually though somewhat irregularly tliroughout
life, and a like diminution apparently obtains in intra-uterine
existence. It seems as if the impetus of growth given at im-
pregnation gradually dies out.

§ 714. The saliva of the babe, very scanty at first and not
abundant until teething begins, is active on starch though less
so than in the adult, and its gastric juice, unlike that of many
new-born animals, has good peptic powers, and its pancreas
good tryptic powers, though apparently the pancreatic action
on starch is feeble. From this we may infer that its digestive
processes are in general identical with that of the adult though
ill suited for any large amount of starch in the food ; and they
are feeble, since the fieces of the infant contain a considerable
quantity of undigested food (fat, casein, &c.), as well as un-
altered bile-pigment, and undecomposed bile-salts.

The heart of the babe, as shewn in the preceding Table, is,
relatively to its body-weight, larger than the adult, and the

Digitized by


Chap, hi.] THE PHASES OF LIFE. 1147

frequency of the heart-beat much greater, viz. about 130 or 140
per minute, falling to about 110 in the second year, and about
90 in the tenth year. Corresponding to the smaller bulk of the
body, the whole circuit of the blood system is traversed in a
shorter time than in the adult (12 seconds as against 22) ; and
consequently the renewal of the blood in the tissues is ex-
ceedingly rapid. Uelatively to the body-weight there is also
considerably more blood in the babe than in the adult. The
respiration of the babe is quicker than that of the adult, being
at first about 35 per minute, falling to 28 in the second year, to
26 in the fifth year, and so onwards. The respiratory work,
while it increases absolutely as the body grows, is, relatively to
the body-weight, greatest in the earlier years. It is worthy of
notice, that the absorption of oxygen is said to be during these
earlier years relatively more active than the production of car-
bonic acid ; that is to say, there is a continued accumulation of
capital in the form of a store of oxygen-holding explosive com-
pounds (cf. § 289). This, indeed, is the strikimg feature of
infant metabolism. It is a metabolism directed largely to con-
structive ends. The food taken represents, undoubtedly, so
much potential energy ; but before that energy can assume a
vital mode, the food must be converted into tissue; and, in such
a conversion, morphological and molecular, a large amount of
energy must be expended. The metabolic activities of the
infant are more pronounced than those of the adult, for the
sake, not so much of energies which are spent on the world
without, as of energies which are for a while buried in the
rapidly increasing mass of flesh. Thus the infant requires over
and above the wants of the man, not only an income of energy
corresponding to the energy of the flesh actually laid on, but
also an income corresponding to the energy used up in making
that living sculptured flesh out of the dead amorphous proteids,
fats, carbohydrates and salts, which serve as food. Over and
above this, the infant needs a more rapid metabolism to keep up
the normal bodily temperature. This, which is no less, indeed
slightly ('80) higher, than that of the adult, requires a greater
expenditure, inasmuch as the infant with its relatively far larger
surface, and its extremely vascular skin, loses heat to a propor-
tionately much greater degree than does the grown-up man. It
is a matter of common experience that children are more affected
by cold than are adults. The bodily temperature is moreover
less stable in the infant than in the adult, and departures from
the normal temperature have not the grave significance they
have in the adult.

This rapid metabolism is however not manifest immediately
upon birth. During the first few days, corresponding to the
loss of weight mentioned above, the respiratory activities of the
tissues are feeble; the embryonic habits seem as yet not to have

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been completely thrown off, and, as was stated in § 306, new-
born animals bear with impunity a deprivation of oxygen, which
would be fatal to them later on in life.

Associated probably with these constructive labours of the
growing frame is the prominence of the lymphatic system.
Not only are the lymphatic glands largely developed and more
active (as is probably shewn by their tendency to disease in
youth), but the quantity of lymph circulation is greater than
in later years. Characteristic of youth is the size of the thymus
body, which increases up to the second year, and may then re-
main for a while stationary, but generally before puberty has
suffered a retrogressive metamorphosis, so that very often hardly
a vestige of it remains behind. The thyroid body is also rela-
tively greater in the babe than in the adult ; the spleen, on the
other hand, relatively to the body-weight does not change
greatly, though rather smaller in the adult. As we have alreaay
said the recuperative power of infancy and early youth is very

The quantity of urine passed, though scanty in the first
two days, rises rapidly at the end of the first week, and in
youth the quantity of urine passed is, relatively to the body-
weight, larger than in adult life. This may be, at least in
?[uite early life, partly due to the more liquid nature of the
ood, but is also in part the result of the more active metabo-
lism. For not only is the quantity of urine passed, but also
the amount of urea and of some other urinary constituents
excreted, relatively to the body-weight, greater in the child
than in the adult. The presence of uric acid, of oxalic acid,
and according to some, of hippuric acid in unusual quantities
is a frequent characteristic of the urine of children. It is
stated that calcic phosphates, and indeed the phosphates gen-
erally, are deficient, being retained in the body for the building
up of the osseous skeleton.

§ 715. It would be beyond the scope of this work to enter
into the psychical condition of the babe or the child, and our
knowledge of the details of the working of the nervous system
in infancy is too meagre to permit of any profitable discussion.
It is hardly of use to say that in the young the whole nervous
system is more irritable or more excitable than it is in later
years ; by which \^
is less rigid, less m
of this work, we h
new-born puppies
various cerebral are
movements ; these
but in this respect (
animals correspond
different kinds of

Digitized by


Chap, hi.] THE PHASES OE LIFE. 1149

the human babe as regards the latter is intermediate between
the puppy and the young guinea-pig. As we have seen, the
fibres of the various tracts in the central nervous system ac-
quire their medulla at different epochs ; there is experimental
evidence in support of the view, otherwise probable, that the
assumption of functional activity follows in the same order ;
and the pyramidal tract is as we have seen the one in which
the fibres are very late in acquiring their medulla. It has
been asserted that in a new-bom animal stimulation of the
vagus produces no cardiac inhibition and that this does not
appear for several days ; other observers however have ob-
tained positive results and that even in the uterus ; probably
in this respect also animals differ. In the human infant the
sense of touch, both as regards pressure and temperature,
appears well developed, as does also the sense of taste, and
possibly, though this is disputed, that of smell. The pupil
(larger in the infant than in the man) acts fully, and normal
binocular movements of the eyes have been observed in an
infant less than an hour old. The eye is from the outset
fully sensitive to light, though of course visual perceptions are
imperfect. Auditory sensations on the other hand, seem to
be dull, though not wholly absent, during the first few days of
life ; this may be partly at least due to absence of air from the
tympanimi and to a tumid condition of the tympanic mucous
membrane. As the cliild grows up his senses sharpen with
constant exercise, and in his early years he possesses a general
acuteness of sight, hearing, and touch, which frequently be-
comes blunted as his psychical life becomes fuller. Children
however are said to be less apt at distinguishing polours than
in sighting objects ; but it does not appear whether this arises
from a want of perceptive discrimination or from their being
actually less sensitive to variations in hue. A characteristic
of the nervous system in childhood, the result probably of the
more active metabolism of the body, is the necessity for long or
frequent and deep slumber.

§ 716. Dentition marks the first epoch of the new life. At
about seven months the two central incisors of the lower jaw
make their way through the gum, followed immediately by the
corresponding teeth in the upper jaw. The lateral incisors,
first of the lower and then of the upper jaw, appear at about
the ninth month, the first molars at about the twelfth month,
the canines at al)out a year and a half, and the temporary den-
tition is completed by the appearance of the second molars
usually before the end of the second year.

About the sixth year the permanent dentition commences
by the appearance of the first permanent molar beyond the
second temporary molar ; in the seventh year the central per-
manent incisors replace their temporary representatives, fol-

Digitized by


1150 DENTITION. [Book iv.

lowed in the next year by the lateral incisors. In the ninth
year the temporary first molars are replaced by the first bi-
cuspids, and in the tenth year the second temporary molars are
similarly replaced by the second bicuspids. The canines are
exchanged about the eleventh or twelfth year, and the second
permanent molars are cut about the twelfth or thirteenth
year. There is then a long pause, the third or wisdom tooth
not making its appearance till the seventeenth, or even twenty-
fifth year, or in some cases not appearing at all.

§ 717. Shortly after the conclusion of the permanent den-
tition (the wisdom teeth excepted) the occurrence of puberty
marks the beginning of a new phase of life ; and the diflference
between the sexes, hitherto merely potential, now becomes func-
tional. In both sexes the maturation of the generative organs
is accompanied by the well-known changes in the body at large ;
but the events are much more obvious in the typical female than
in the aberrant male. Though in the boy, the breaking ©f the
voice and the rapid growth of the beard which accompany the
appearance of active spermatozoa, are striking features, yet they
are after all superficial ; and though, as we have seen (§ 713),
the curves of his increasing weight and height undergo before
and at this period, characteristic variations, the general events
of his economy pursue for a while longer an unchanged course ;
the boy does not become a man till some years after puberty ;
and the decline of his functional manhood is so gradual that
frequently it ceases only when disease puts an end to a ripe old
age. With the occurrence of menstruation, on the other hand,
at from thirteen to seventeen years of age, subsequent to the
acceleration of growth noted above § 713, which indeed appears
preparatory to it, the girl almost at once becomes a woman, and
her functional womanhood ceases suddenly at the climacteric in
the fifth decennium. During the whole of the child-bearing
period her organism is in a comparatively stationary condition.
The variations in the yearly increment of the girl before puberty
though not so marked are more complex than those of the
boy, and she reaches the maximum of yearly increment sooner
than does he ; during this whole period indeed she precedes
him in growth and she has nearly reached her maximum, while
he is still continuing
nineteenth year onwa
being followed subse(
the man reaches his
woman is at her great

Of the statical difl
of the pelvis, and th
rectly connected wit
have only an indirect
least of nearly all the


Chap, hi.] THE PHASES OF LIFE. 1151

The baby boy is heavier and taller than the baby girl, and the
maiden of five breathes with her ribs in the same way as does
the matron of forty. The woman is lighter and shorter than
the man, the limits in the case of the former being from 1*444
to 1-740 metres of height and from 39*8 to 93-8 kilos of weight,
in the latter from 1-467 to 1-890 of height, and from 49-1 to
98-5 kilos of weight. The muscular system and skeleton are
both absolutely and relatively less in woman, and her brain is
lighter and smaller than that of man, being about 1272 grammes
to 1424. Her metabolism, as measured by the respiratory and
urinary excreta, is also not only absolutely but relatively to
the body-weight less, and her blood is not only less in quantity
but also of lighter specific gravity and contains a smaller pro-
portion of red corpuscles. Her strength is to that of man as
about 5 to 9, and the relative length of her step as 1000 to

§ 718. From birth onward (and indeed from early intra-
uterine life) the increment of growth as we have seen, though
undergoing certain variations, continues to diminish. At last
a point is reached at which the curve cuts the abscissa line, and
the increment becomes a decrement. After the culmination of
manhood at forty and of womanhood at the climacteric, the
prime of life declines into old age. The metabolic activity of
the body, which at first was sufficient not only to cover the
daily waste but to add new material, later on is able only to
meet the daily wants, and at last is too imperfect even to sus-
tain in its entirety the existing frame. Neither as regards
vigour and functional capacity, nor as regards weight and
bulk, do the turning-points of the several tissues and organs

Online LibraryArthur Sheridan Lea Sir Michael FosterA text book of physiology → online text (page 126 of 148)