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reflex ; moreover, the effect is stopped by section of the sciatic, and hence
is not of peripheral origin as a result of heating of the terminal apparatus.

Certain drugs, especially picrotoxin and strychnia, appear to cause
sweating exclusively by their action on the spinal cord. Nicotine and
eserine cause slight sweating after section of the limb nerves, and are
therefore not exclusively, though mainly, central stimulants.*

Eeflexly, it may be broadly stated that stimulation of almost any
afferent channel will cause sweating. A cat will sweat on the pads of
its feet at the sight of a dog, mustard in the mouth causes sweat on the
foreheads of many persons, and the application of heat to the skin is a
familiar cause of increased action of the glands. According to Greiden-
berg,^ in a patient with sweating legs, slight skin stimuli diminished the
secretion, while strong stimuli caused an increase.

Directly from the periphery, the sweat-glands may be excited by
certain drugs or by raising their temperature.

Pilocarpine excites secretion of sweat after complete division of the
nerves, and localised secretion may be produced by introducing it
beneath the skin. Its action is probably in the main upon the termina-
tions of the nerves in the glands, since it is, as a rule, non-effective, when
sufficient time has been allowed to elapse after section of the nerves to
ensure complete degeneration (Luchsinger, Nawrocki, and Vulpian). On
the other hand. Max Levy ^ states that pilocarpine may still give good

1 Bloch, "These de Paris," 1880.

" " Yerhandl. d. Berl. physiol. Gesellsch.," in Arch. f. Physiol., Leipzig, 1895, S. 198.

^ Luchsinger, Arch. f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 369. ; Robillard,
"These de Doct.," Lille, 1880.

''Luchsinger, Arch. f. d. ges. Physiol., Bonn, 1877, Bd. xv. S. 482; Hogyes, ref. in
Jahresh. ii. d. Fortschr. d. Anat. u. Physiol., Leipzig, 1881, Bd. ix. S, 72.

^ Jahresh. ii. d. Fortschr. d. Anat. u. Physiol., Leipzig, 1882, Bd. x. S. 81,

8 Centralbl.f. Physiol., Leipzig u, Wien, 1892, Bd, v, S. 68.



68o S£ CRETION AND ABSORPTION B Y THE SKIN.

secretion, when excitation of previously divided nerves is without effect,
pointing to stimulation of the gland protoplasm by the drug.

According to Eossbach,^ small doses act upon the nerve-endings,
while large doses also affect the gland protoplasm ; and some of the
experiments of Luchsinger, Marme, and Hogyes, in which pilocarpine
caused secretion, long after the time necessary for complete degeneration
of the nerves had elapsed, point to the same conclusion.

There appears to be no central action by pilocarpine, for Eobillard,^
after separating the foot of a cat from the body, with the exception of
the tibial nerve, obtained no secretion of sweat on injection of pilo-
carpine into the general circulation ; though the nerve was proved to
conduct, by a profuse sw^eat caused on asphyxiation.

Muscarine ^ also acts as a peripheral excitant, but is less active than
pilocarpine.

Atropine and duboisine are both antagonistic to pilocarpine and
muscarine.

In the cat an injection into a vein of 3 mgrms. of atropine is sufficient
to make stimulation of the sciatic ineffective ; subsequent intravenous
injection of 10 mgrms. of pilocarpine will cause sweating, though the
nerve is still without action on excitation. In such a case the atropine
poisons the nerve-ending, but the gland protoplasm is still excitable and
responds to pilocarpine. According to Eossbach,* a dose of 20 to 30
mgrms. of atropine is needed, in the case of a cat, to paralyse the gland-
cells to such an extent that subsequent local application of pilocarpine
is without effect. All glandular apparatus appears to be far more
sensitive to atropine than to pilocarpine.

The local paralysing effect of atropine was elegantly demonstrated
by Aubert.^ If the palm or finger (carefully cleaned) is pressed on to
paper sensitised with silver nitrate, the spots of chloride formed at the
mouths of the sweat-ducts are quite visible. If the experiment is tried,
after a pad soaked in atropine solution has been tied over a limited
surface overnight, that surface is found to yield no spots, in contrast to
the surrounding field.

Finally, the terminal sweat apparatus is very sensitive to change of
temperature. Luchsinger ^ has shown that not only cold but excessive
heating retards the action of the glands. Thus if, on a warm day, one
hand be held in water at 45° to 50° C. for ten minutes, while the other is
immersed in water at 15° to 30° C, and exercise is then taken, the hand
which was in water at the lower temperature commences to sweat at
once, the other not for some considerable time. In experimental work,
in which the excitation of nerves is undertaken and the outbreak of
sweat observed, the greatest caution is necessary to keep the tempera-
ture of the extremities constant, for with a cold foot a nerve root hold-
ing sweat-filires in reality, may be wrongly considered to hold none, if
the terminal apparatus is depressed by cold.

That the formation of sweat is a true act of secretion, and not
merely filtration, is shown by experiments already quoted, in which it is
noted that after stoppage of the circulation sweat is still secreted on

1 Arch. f. d. ges. Physiol., Bonn, 1880, Bd. xxi. S. 1. '^ Loc. cit.

" Triimpy and Luchsinger, Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xviii. S. 501 ;
Ott and Wood Field, Journ. Physiol., Cambridge and London, 1878, vol. i. p. 193 ;
Hogyes, loc. cit.

* Loc. cit. s Xt/ow m6d., 1874.

^ Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xviii. S. 478.



ELECTRO-MOTIVE PHENOMENA IN SKIN GLANDS. 68 1

excitation of nerves ; and further, by the fact that by means of atropine
the secretion of sweat can be stopped in spite of the continued circula-
tion of the blood.

It is probably right to conclude that the blood supply is a necessary
adjuvant to the prolonged activity of the gland-cells, but not the stimu-
lant to their action, though, according, to Levy,^ secretion is provoked
upon reinstallation of the circulation, in a limb with cut sciatic, which
has been long kept anaemic. This effect may possibly be due to the
mechanical stimulation of the glands by the pulse.

Levy Dorn'-^ placed the hind-limb of a cat in a receptacle within
which the air pressure could be raised, and found that the secretion
could overcome a pressure in excess of that in the large arteries.

Nothing is definitely known as to the existence or not of any
action of the nervous system upon the sebaceous glands.

According to Arloing,^ section of the cervical sympathetic in
donkeys causes exudation of sebum from the sebaceous glands of the
skin of the ear, reaching its maximum fifteen hours after section, and
lasting for sixty-four hours. Stimulation of the peripheral end of the
nerve also causes secretion from these glands.

The glands of the skin of the frog undergo periodic contraction and expan-
sion by means of their muscular sheaths,'' and have been carefully studied by
Engehiiann,^ Strieker and Spina,^ and Drasch,'^ in the web and memhrana
nictitcms. The spontaneous movements in the case of the web glands are
stopped temporarily by section of the sciatic, or seventh, eighth, and ninth
anterior spinal roots. Excitation of the sciatic or reflex stimulation of the skin
leads to contraction of the glands, as also does direct excitation by vapours of
chloroform or ether, or by carbonic acid gas. During contraction of the whole
gland, by its muscular sheath, the lining gland-cells swell, and, according to
Drasch, in the case of the memhrana nictitans, the fifth cranial nerve, on ex-
citation, causes contraction of the sheath only, while excitation of the sympa-
thetic causes swelling of the cells. Pilocarpine causes increased secretion by
these glands. Strieker and Spina advanced a theory of secretion based upon
observations of these glands, maintaining that, in the act of swelling, fluid is
sucked in by the cells from the surrounding lymph spaces, and on contraction
forced out into the lumen ; the theory obviously involves the assumption of some
valvular structure in the protoplasm, of which we know nothing, and furthermore
has been disposed of by Drasch, who has found that the glands of the mem-
hrana nictitans may secrete freely in stages of immobility of the lining cells.

In the case of fish — in the eel it has been shown that the secretion of the
goblet cells of the epidermis and of the club cells (when present) is under the
influence of the nervous system, but the nerve paths have not been worked out.^

Electro-motive Phenomena in Skin Glands.

In attempting to demonstrate the existence of currents in the
uninjured muscles of the frog, du Bois Eeymond ^ discovered that the

■^ Loc. cit.

^ " Verhandl. d. BerL physiol. Gesellsch.," Arch. f. Physiol., Leipzig, 1893, S. 383.

^ Arch, de physiol. norm, etyath., Paris, 1891, S6-. 5, tome iii. p. 241.

'' Ascherson, Arch. f. Anat. u. Physiol., Leipzig, 1840, S. 15.

5 Arch./, d. ges. Physiol., Bonn, 1872, Bd. v. S. 498.

^ Sitztmgsb. d. k. AJcad. d. Wissensch., Wien, 1880, Bd. Lxxx. Abth. 3, S. 9.5.

■^ Arch./. Physiol., Leipzig, 1889, S. 96.

"^ Reid, Phil. Trans., London, 1894, voL clxxxv. p. 319.

^ " Untersuch. iieber thierische Elektricitat," Bd. ii. Abth. 2, S. 9-20.



682 SE CRE TION AND ABSORPTION B Y THE SKIN.

skin itself is a seat of electro-motive force, which he located in the
glands. The current is in the direction from the free to the deep sur-
face, the former being electrically negative to the latter. A current so
oriented may be termed " ingoing," and is the normal direction of the
" current of rest " of all secreting membranes, so far investigated.

The discovery was corroborated by Rosenthal,^ and extended to the
case of the stomach and gut mucosae in the frog and rabbit, while
Hermann 2 found a similar current in the skins of many fish, and,
more recently, in the tree frog, proteus, and axolotl.^ Such currents as
a rule exhibit spontaneous variations in intensity, especially in the case
of the skin of the frog.

Valentin,* and later Eoeber,^ furthermore found that in the case of
the frog's skin excitation of the cutaneous nerves causes a variation in
the electro-motive force of the resting skin, and the latter observer
that this phenomenon could be produced by reflex excitation, and
was not abolished by curare.

The direction of the " current of action " evoked by excitation of
nerves was not found to be constant by Eoeber, a fact corroborated by
all subsequent investigators. Thus Engelmann^ observed a double
excitatory variation of the " current of rest," namely, an outgoing
followed by an ingoing current (negative followed by positive
variation), while Hermann ^ noted an ingoing " current of action,"
often preceded by an outgoing current of short duration, and Bayliss
and Bradford ^ state that it is " scarcely possible to speak of a normal
excitatory variation."

Hermann and Luchsinger^ found that the cat's foot also gave an
ingoing " current of rest," but that the current developed on excitation
of the sciatic was constantly ingoing, and prevented from development
by the exhibition of atropine.

Luchsinger ^'^ demonstrated the existence of exactly similar currents
in the snout of the pig, goat, cat, and dog on excitation of the cervical
sympathetic or infra-orbital nerve, and Hermann and Luchsinger ^^ in the
tongue glands of the frog, though in the latter case excitation of the
hypoglossal or glossopharyngeal nerve gave a triphasic " current of
action," an outgoing being interpolated in a long lasting ingoing
phase. Tarchanofi" ^^ has further indicated that parts of the skin of
man rich in sweat-glands {e.g. palm of hand), are negatively electrical
to parts poor in sweat-glands {e.g. skin over deltoid), and that the
ingoing " current of actioii " of such glands can be excited refiexly by
very slight stimuli, such as sound or even the expectation thereof,
odours, or mental effort.

The well-known Willkilrversuch of du Bois Eeymond, in which,
when the index -fingers of the two hands are immersed in vessels of
liquid in circuit with a galvanometer, a voluntary effort of the

1 Arch./. Physiol., Leipzig, 1865, S. 301.

2 Areh.f. d. ges. Physiol., Bonn, 1882, Bd. xxvii. S. 280.
^ Ibid., 1894, Bd. Iviii. S. 242.

■* Ztschr.f. rat. Med., 1861, Bd. xv. S. 208.

=^Arch.f. Physiol., Leipzig, 1869, S. 633.

^Areh.f. d. ges. Physiol., Bonn, 1872, Bd. vi. S. 97.

"^ Ibid., 1878, Bd. xvii. S. 291 ; and 1882, Bd. xxii. S. 280.

^ Journ. Physiol., Cambridge and London, 1886, voL vii. p. 223.

9 Areh.f. d. yes. Physiol., Bonn, 1878, Bd. xvii. S. 310.

" Ibid., 1880, Bd. xxii. S. 152. ^^ Ibid., 1878, Bd. xviii. S. 460.

^'- Ibid., 1890, Bd. xlvi. S. 46.



ELECTRO-MOTIVE PHENOMENA IN SKIN GLANDS. 683

muscles of one forearm {e.g. grasping a rod) gives a current passing up
the contracting arm, is probably to be explained by the concomitant
excitation of the sweat-glands on the side of action.

Not only in the case of membranes containing complex glands is an
ingoing " current of rest " observed, but also in secreting membranes
supplied with unicellular glands (goblet cells), as the pharynx and
cloaca of the frog,^ or the skin of the fish ; ^ and furthermore, in certain
membranes, quite free of secretory structures, and covered only by
stratified epithelium, such as the skin of the pigeon and the mucosa of
the crop of the same bird in winter.^

The attempts to explain the causation of the above currents, it must
be confessed, have not been very satisfactory.

As regards the constantly observed ingoing " current of rest," it is
obviously of the first importance to determine whether it is of purely
epidermic origin, of purely glandular origin, or whether it receives a
component from both sources. The experiments with the non-glandular
skin of the bird above-mentioned show that simple stratified epithelium
can give rise to such a current, and Hermann * has further proved that
shaving the epidermis of the cat's foot lowers the electro-motive force of the
" current of rest." Furthermore, Bach and Oehler ^ found that pencilling
the skin of the frog with solution of corrosive sublimate abolished the
" current of rest," though the excitatory change from the glands beneath
could still be obtained by exciting the nerves of the skin.

On the other hand, it can hardly be denied that in such cases as
the gastric mucosa of the frog, where the epithelium is practically all
converted into unicellular glands (goblet cells), the marked ingoing
" current of rest " is of glandular origin,® and this must also be the case
in such a membrane as the cloacal mucosa of the frog.

It is simplest, in the present state of knowledge, to admit that both
stratified epithelium and gland protoplasm can give rise to currents.

Hermann and Biedermann consider such currents due to alteration
of metabolic activity in the continuity of protoplasm. Protoplasm
becoming " altered " to mucus in a goblet cell is negative electrically to
the unaltered material at the base of the cell, and the same in the
process of keratinisation in the continuity of epithelium. Since altered
parts are negative electrically to unaltered or less altered, the result will
be an ingoing current, whether we choose the glands or the epidermis,
or both, as the source of the electro-motive force of the " current of rest."

If we turn to the case of the " action current," it is only in the case
of the mammalian glands that any clear explanation on the above
hypothesis is feasible. In these glands, as already mentioned, the
" current of action " is purely ingoing, and it is only necessary to assume
that in action the " difference " between the base and the free border of
the cells becomes more marked than at rest, with a concomitant develop-
ment of electro-motive force with ingoing current.

In the skins and other secreting membranes of amphibians and fish,
we are met with the difficulty that it is not possible to predict with
certainty what will be the direction of the " action current " elicited by

1 Biedermann, ibid., 1893, Bd. liv. S. 209.

^ Hermann, loc. cit. ; Reid, Phil. Trans., London, 1893, Bd. clxxxiv. p. 335.

^ Reid, Journ. Physiol., Cambridge and London, 1894, voL xvi. p. 359.

■* Arch./, d. ges. Physiol., Bonn, 1894, Bd. Iviii. S. 242.

5 Ibid., 1880, Bd. xxii. S. 30. 6 Bohlen, ibid., 1894, Bd. Ivii. S. 97.



684 SECRETION AND ABSORPTION B Y THE SKIN

excitation of the nerves. The strength of the stimulus, and the extent to
which the normal ingoing " current of rest " is developed, alfects the result,
and hypotheses have been based upon both of these factors of the case.

Herraarm ^ long ago suggested the possibility of augmenting and inhibitory
fibres to the glands, and in his most recent publication^ still entertains the
idea. On the other hand, Biedermann suggests that the two sides of protoplasmic
activity (the katabolic and anabolic) in the secretory cells are associated with
generation of electro-motive force, causing currents in opposite directions
in the two cases ; that the electro-motive force of the " current of rest " is
the algebraic smn of these opposing forces at the moment ; and that the results
of nerve excitation are related directly to the ascendancy of one or the other
metabohc action at the time of stimulation.

The production of an outgoing " current of action " is considered by
Biedermann as due to the nerve excitation provoking an excess of anabolic action
in the cell, that of an ingoing " current of action " as due to excess of katabolism,
so that one and the same class of nerve-fibre is supposed to produce quite
opposite results in the cell, the effect being partly conditioned by the state of
the balance in the cell between the two processes at the moment of excitation,
and partly by the strength of the stimulus. He supposes that the cell process
least developed at the time of excitation, tends to be stunulated in excess of its
fellow, so that if the ingoing "current of rest" is weak, as a result of slight
katabolic ascendancy, excitation tends to cause an ingoing " current of action " ;
and, vice versa, if the ingoing " current of rest " is strong, as a result of marked
katabolic ascendancy, the result of excitation of the cell is liable to be the
development of an outgoing " current of action."

Hermann objects to tbis, that if the electrical sign of excess of anabolism
over katabolism is plus, the induction of such a condition must start from the
deep ends of the cells, i.e. from the ends from which they get their pabulum
from the blood, and excess of positivity of this end of the cell comes, so far as
the direction of current is concerned, to the same thing as excess of negativity
at the free end of the cell, associated by hypothesis with katabolic ascendancy,
and should develop a current in the same direction, i.e. ingoing.

It may also be noted in this connection, that, according to Bohlen,^ in
the gastric mucosa of mammals, cessation of circulation or any interference
with blood supply tends to convert the normal ingoing into an outgoing
" current of rest." If an outgoing current is associated with excess of anabolism
over katabolism, it is difficult to conceive how withdrawal of blood supply can
induce such a change. A similar complete reversal of the direction of the
" current of rest " is obtainable in the secreting membranes of the frog and
fish by abstraction of heat, or by narcotisation with carbonic acid gas, ether,
or chloroform.

A strong stimulus of a nerve trunk may, in practice, cause an outgoing
action current, and a weak stimulus one that is ingoing, but it is again difficult
to conceive that difference in the strength of stimulus of one class of nerve-
fibre can alter the whole character of the metabolism in the cells.

Hermann was at one time of opinion that the two kinds of glands in the
frog's skin might be associated with the two phases of the excitatory variation ;
and the lip of the eel, which contains no club cells but only goblet cells, gives
an outgoing " action current," while the body skin, rich in club cells and poor in
goblets, gives an ingoing " action current " with the same strength of stimulus ; "^
but since the cloacal or jDharyngeal mucosa of the frog, containing only one sort
of secretory cell, and the non-glandular crop of the Aviuter pigeon, can give
currents in 1)oth directions, the hypothesis is not of universal application.

^Arch.f. d. gcs. Plajsiol., Bonn, 1878, Bd. xvii. S. 303.

2 Ibid., 1894, Bd. Iviii. S. 242. = i^^^ ^ii_

* Reid and Tolputt, Journ. Physiol., Camljridge and London, 1894, vol. xvi. p. 203.



ABSORPTION B Y THE SKIN IN MAN. 685

Absorption by the Skin.

Man. — To decide the case for or against the possibility of absorption
by the human skin, would appear a simple problem, yet a literature
reaching back over a century indicates that the production of un-
impeachable testimony on either side has proved a matter of no little
difficulty.

A tiuid in contact with the skin is separated from the blood vessels
by layers of epidermic cells with intercellular spaces, but since the
superficial cells (except in the palm of the hand and sole of the foot)
are greasy with sebum, one of the first conditions for absorption is that
the fluid shall be able to wet the surface, so that imbibition l;)y the cells,
or entrance of the fluid into the capillary spaces between them, may
take place. Though lanoline, the natural fat of the skin, takes up
water, such action only occurs slowly, and unless the skin is soaked
long in warm water, it is a familiar observation that it does not easily
become sodden, except in the case of the palms and soles. It is there-
fore not to be expected that water or watery solutions will be capable
of absorption by the skin of man, and the experimental evidence is
distinctly against such an assumption.

The method of some of the older observers, of attempting to decide
the question of absorption of water by immersing a man in a bath after
weighing, and weighing again after a prolonged sojourn therein, w^e may
dismiss by a bald statement of obvious sources of error.

{a) There is no guarantee that the normal loss of weight of the body
per unit time, through lungs and skin, is the same during the bath as
estimated during preceding hours. (The experiments showed, in different
instances, gains, losses, and absence of change of weight.) ^

Further, mere soakage of the epidermis of palms and soles may
mask an actual loss of weight in the bath.'^

(&) It is impossible to be certain that the epidermis of the whole
body is devoid of fissures through which water might reach the deeper
parts.

(c) It is difficult to totally exclude absorption by immersed mucous
surfaces.

(f?) A balance sensitive enough to indicate a difference of a few
grammes on a weight of many kilos., is difficult to construct.

{e) A considerable loss of surface epidermis occurs in " drying " the
body with a toweL

An improvement upon the method of total immersion is that of
immersion of a part of the body, but the vessel, instead of being
weighed before and after immersion of the part of the body, as in the
experiments of Vierordt and Eichberg,^ is better graduated as in the
experiments of Falck,^ or provided with a capillary pipette, by means of
which absorption can be determined by fall of level of fluid,^ because,
by the gravimetric method, the error from mere soakage of epidermis
becomes far larger than in the volumetric method, though here also a
slight diminution in volume accompanies imbibition by the palm or sole,

^ Jamin et de Lauras, Compt. rend. Acad. d. sc, Paris, 1872, tome Ixxv. p. 60.
2 Poulet, Hid., 1856, tome xlii. p. 435.

'^ Arch. f. physiol. Heilk., Stuttgart, 1856. ■^ Ibid., 1852.

^ Madden, "An Experimental Inquiry into the Physiology of Cutaneous Absorption,"
Edinburgh, 1838; Fleischer, Inaug. Diss., Erlangen, 1877.



686 SECRETION AND ABSORPTION B Y THE SKIN.

if an arm or leg be used, since the combination of a body with water in
which it is soaked is accompanied by contraction, so that the total
volume after soakage is less than the sum of the initial volumes.^

Fleischer could obtain no positive evidence of absorption of water
by the skin of the arm, immersed in a Mosso's plethysmograph (pro-
vided with a capillary pipette) for three hours.

Solutions of chemical substances easily detected in the secretions
have been much employed, a part of the body being immersed, or the
solution applied by means of a spray. Colouring matters, inorganic



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