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goats, has also been found to increase the fat of milk.'^

It does not, of course, follow that because an excess of a particular organic
principle in the food produces an increase of certain constituents of the milk,
that these constituents are directly produced from such material, for the effect
may be produced indirectly by the functions of the gland-cells becoming
modified, according to the nature of the pabulum they are receiving. Looked

1 Hammarbacher (goat), Arch. f. d. ges. Physiol., Bonn, 1884, Bd. xxxiii. S. 228 ;
Conievin {C'o7npt. rend. Soc. de bioL, Paris, 1891, p. 628) found that in the cow the amount
of milk yielded was not influenced by the daily injection of 0*25 grm. pilocarpine. See
also Mironow, loc. cit.

- Hammarbacher, loc. cit.

" The evidence for this is given by Heidenhain (Hermann's " Handbuch," 1882, Bd. v.).
where also all the most important references on the influence of diet up to that date will be
found. The following may also be cited — W. Kirchner, Milchzeitung , 1891, Bd. xx. ;
C. Schneider, " Einliuss versch. Fiitterung auf d. Zusammensetz. der Milch," Diss.,
Leipzig, 1893.

■* See article on "Metabolism."

^ Ssubotin, VIrchow's Archiv, 1866, Bd. xxxvi. ; Centralhl. f. d. med. Wissensck., Berlin,
1866, S. 337; Kemmerich, ibid., S. 467; Kuhn, Journ. f. Landwirthsch.,l?>l&, S. 381;
Weiske, ibid., 1878, S. 447 ; Cf. also Juretschke, " Einfluss versch. Oelkuchensorten auf
dem Fettgehalt der Milch," Diss., Leipzig, 1893.

•^ L Munk, Arch. f. wissensch. v,. pralct. Thierh., Berlin, 1881, Bd. vii. S. 91.

''Stumpf, DeuiscJies Arch. f. klin. Med., Leipzig, 1882, Bd. xxx. S. 201.



FORMATION OF THE ORGANIC CONSTITUENTS. 665

at in this light, certain substances may be said to stimulate the cells of the glands
to increased activity in all directions, tending to the production of a larger
quantity of milk rich in all kinds of solid constituents ; whilst other substances
may be looked upon as stimulating the cells in a special manner, tending
to the increased production of certain only of the constituents of the milk.

Place of formation of the organic constituents. — As already
noticed, the fact that the chief organic constituents of the milk are
peculiar to the secretion, and do not occur as such in the blood or
lymph, may be regarded as sufficient evidence of their being formed in
the gland itself.^ The casein is in all probability produced by a mole-
cular change in the composition of the serum albumin or globulin,
which is supplied to the cells from the blood or lymph. The fat may
be formed by the cells of the gland from proteid, or possibly even from
carbohydrate materials furnished by the blood ; or it may be taken up
directly from fat which has been formed elsewhere, and which is always
present in a certain small amount in blood and lymph. For while, on
the one hand, there exists no clear evidence to show that the mammary
gland can itself manufacture fat, it is extremely probable that, in
common with most if not all other cells in the body, the cells of this
gland do possess such a faculty. With regard to the characteristic
sugar of the secretion, and which, being characteristic, must be pro-
duced by the gland itself, there is some evidence to show that this is
formed from dextrose, which is itself manufactured elsewhere than in
the gland. That this is so would appear from the following experiment
by Paul Bert.'^ Bert removed the mammary glands from goats,
then allowed them to become pregnant. After parturition, the
urine, during three days, contained a substance which reduced cupric
oxide and appeared to be dextrose. This was not present before par-
turition, nor was it found in normal animals either before or alter
parturition ; it was therefore presumably formed in the organism in
larger amount than usual for the purpose of becoming converted into
lactose in the mammary gland.

In view of the fact that lactose is frequently found in the urine in women,
and in mammals generally, immediately before and after parturition,-^ this
experiment of Bert seems to need repetition, especially since he appears not to
have isolated or carefully examined the reducing substance which he detected.
The lactose found in the urine after parturition has generally been supposed
to be re-absorbed from the secretion which has formed in the alveoli and ducts
of the mammary glands.

Thierf elder ^ has pointed out that both the casein and sugar of milk could
be derived from the nucleo-proteids or glyco-proteids of the gland-cells by a
process of splitting. In support of this view, a formation of lactose is said to
occur on keeping portions of minced fresh mammary gland in normal saline
solution at the temperature of the body ; the lactose being preceded by a colloid
carbohydrate, identical, according to Landwehr,^ with his " animal gum." This,
however, does not affect the question of the ultimate sources of origin of these

1 A small quantity of casein is said to occur in the secretion of the sebaceous glands
(JSTeumeister, "Lehrbuch," Aufl. ii. S. 496). This is of interest in connection with
the fact that the mammary glands have Taeen regarded as representing enlarged and
modified sebaceous glands.

" Compt. rend. Acad. d. sc, Paris, 1884, tome xcviii. No. 13.

■' Hofmeister, Ztschr.f.physiol. Chem., Strassburg, 1878, Bd. i. S. 101.

^Arch.f. d. ges. Physiol., Bonn, 1883, Bd. xxxii. S. 619.

^ Ibid., 1887, Bd. xl. S. 21.



666 MECHANISM OF THE SECRETION OF MI IK.

constituents, which are probahly, as already stated, the proteids and carbo-
liydrates derived from the food.

As to the manner in which the secreted materials of the milk
pass out of the secretory cells. — If we ]3ut aside, as resting upon no
solid basis of fact, the suggestion of Striclver, whicli was taken up more
seriously by Eauber,^ that the organic materials of the milk are carried
into the alveoli by emigrated leucocytes, which there break down and set
free their proteid, fatty, and other constituents, we find ourselves face
to face with three possible methods by which the secreted materials
which are formed and accumulate within the gland -cells may pass into
the lumen of the alveoli. The three methods are as follows : —

1. The cells may, as in the case of the sebaceous glands, bodily
break loose, and, becoming detached and disintegrated, set free their
contents within the alveoli.

2. A part only of each cell, namely, the free end, may break loose,
become detached, and disintegrate.

3. The cells may extrude their secreted materials into the alveoli, much
as in the case of other secretions, without undergoing any histological
disintegration.

Of these three views, the first has found support mainly on the ground
of the analogy with what happens in the case of the sebaceous glands of the
skin (with which the mammary glands might be looked upon as in a certain
sense homologous), in which such a complete disintegration of the whole
cell occurs, its place being supplied by another cell, which is produced by
cell-division. Moreover, the colostrum corpuscles have been regarded as
examples of such detached cells filled with secretion, which have not
become disintegrated. Those corpuscles, however, as we have seen, are
rather to be looked upon as of the nature of leucocytes than as epithelial
cells ; nor do we find such evidence of cell multiplication in the mamm.ary
gland as would be at all sufficient to account for the very large number
of cells which would have to become detached in order to furnish the
organic constituents of the secretion. Heidenhain ^ has calculated that
the gland-cells would have to be totally renewed five times in the
course of every twenty-four hours, in order to yield the solids of the
milk. The second view may be looked upon as, in a sense, a modifica-
tion of the first one. It was due originally to Langer, and has been
ably advocated by Partsch and Heidenhain.^ According to this
view, the secretion products which are formed in the gland become
gradually accumulated within the free ends of the cells, which in the
meanwhile lengthen out, and in place of being flat or cubical become
columnar and project into the lumen of the alveolus. The enlarged free
end is then supposed to burst or to become detached and disintegrated,
and thus to set free the accumulated products, while the fixed ends of
the cells (with the nuclei) are supposed to remain, ready to again go
through a similar process.

The evidence adduced in favour of this view is chiefly of a histological
nature. It is the case that in some alveoli of glands in full secretion,
the cells are occasionally seen projecting somewhat prominently into
the lumen ; and it is certainly the case also that the cells, and perhaps
especially such prominent parts, contain fatty globules, similar in

^ " ITfjlif-r den ITr.s]irnng der Mileli," Leipzig, 1879.

- Loc. ciL ^ Vide Heidenhain, n]7. cit.



THE DISCHARGE OF MILK. 667

appearance to those of the milk. Nevertheless, it must be admitted
that such appearances, although they may occasionally be seen, are
decidedly rare. It is so much more common to see, even in the most
actively secreting glands, the alveolar cells uniformly flattened, or at most
very slightly projecting,that I should not hesitate to say that the columnar
appearance, which has been described and figured by Heidenhain, is
quite exceptional, and is in all probability due to the alveoli in which
it occurs being collapsed. Every histologist is aware of the extreme
differences in shape which are produced in epithelial cells by altera-
tions in the conditions of the surface which they cover. Thus, even
the extremely flattened epithelial cells which line the blood vessels
may, when examined in sections of vessels which have been hardened in
a contracted and collapsed condition, project like columnar epithelium
cells into the lumen of the vessel. And the differences in height of
the cells lining the alveoli of the mammary glands may very well be
similarly produced. This is indeed rendered probable from the observa-
tion of Heidenhain,^ that in different lobules of a gland the cells vary
in height, but in the same lobule they have the same height ; and by
the additional observation of the same observer, (<x) that in a bitch
which was suckling seven vigorous puppies the cells were very high ;
(&) that in another well-fed milch bitch, which was not sucked for
forty-eight hours, they were remarkably low ; for the alveoli in these
cases would be flaccid and tense respectively.

The histological evidence in favour of this view^ must therefore be
admitted to be extremely weak, nor, except perhaps in the case of the
unicellular glands of some invertebrates, and the similar unicellular
secreting structures which form the mucus-secreting goblet-cells of verte-
brates, is there any analogous instance of the extrusion of a secretion
by the breaking down of part of the gland-cells. Moreover, the
argument which was used by Heidenhain against the first view, that
it would involve the renewal of the substance of the epithelial cells of
the mammary gland five times in twenty-four hours, will apply with
slight modification equally to the second, and adds a further consider-
able difficulty to its acceptance.

The third view, on the other hand, has the analogy of nearly all
the other secretory structures to support it. It involves no necessity
for assuming such an enormous building up and breaking down of
protoplasm as is required for the other two ; and although we must
admit that the present state of our knowledge does not permit us
to understand how and why it is that certain substances are formed
in these cells, and pass from them into the lumen of the alveolus, the
same admission must be made for all other secretions. Nor is the fact
that the fat of the milk is extruded from the cells in an undissolved
condition any obstacle to the acceptance of the view in question, since
it is probable that the granules which are found in many other secretory
cells {e.g. those of the salivary glands), and which are passed into the
lumen of the alveolus, are extruded as granules, and are first dissolved
in the secretion outside the cells.^

^ hoc. cit.

" The microscopical changes in the cells of the mammary gland during secretion have
been recently made the subject of study by Steinliaus {Arch. f. Physiol., Leipzig, 1892,
Suppl., S. 54) and Szabo {ibid., 1896, S. 32). The former finds evidence of frequent mitotic
division of the cell nuclei (without subsequent division of the cells), and of transforma-



668 MECHANISM OF THE SECRETION OF MILK.

The discharge of milk. — The discharge of milk from the ducts,
which is produced by the action of sucking or milking, is partly the
result of direct mechanical pressure upon the gland, and especially
upon the milk reservoirs of the larger ducts, partly due to a con-
traction of the plain muscular tissue which accompanies these ducts,
and which appears to be set in action by mechanical stimulation
of the nipple. The plain muscular tissue occurs also in the nipple
itself in some abundance, and by its contraction causes a kind of
erection and increased prominence of the nipple. This probably serves
the purpose of keeping open the mouths of the gland-ducts which open
upon the rounded apex of the nipple, thus allowing of the free outflow
of the secretion.^ The flow is also in all probability assisted by a xis
a tergo, derived from the swelling of the whole gland by the reflex
dilatation of its arterioles, and consequent increase of capillary pressure,
and of lymph exudation ; and, to a slight degree also, by newly secreted
milk, which begins to be formed by the gland-cells, in response either
to this increased supply of blood and lymph, or to reflex secretory
influences passing directly to the gland-cells.^

tion of the nuclear substance into fat. The latter could find no mitoses during lacta-
tion, although he found two or three nuclei in each cell. He also describes the accumula-
tion in the cells of albuminous granules which undergo peculiar changes of form, and
are ultimately extruded into the alveoli and there dissolved. These observations require
corroboration.

1 Cf. Hellier "On Nipple Eeflex," Brit. Med. Journ., London, Nov. 7, 1896.

" Cf., however, what has been already said on this subject on p. 663.



SECRETION AND ABSOEPTION BY THE SKIN.

By E. Waymouth Eeid.

CojSTTE^^ts : — Chemical Nature of Skin Secretions, p. 669 — The Secretion of Sweat,
p. 676 — Electro- Motive Phenomena in Skin Glands, p. 681 — Absorption by the
Skin of Man, p. 685~Of lower Mammals, p. 688— Of the Frog, p. 690.

Skin Secretions.

Comparative. — The secretions of the skin in vertebrates fall readily
into two main classes — («) Those in which a watery solution is elabo-
rated by the gland-cells, and (h) those in which products of metamor-
phosis or degeneration of the gland-cells themselves form the secretion.

As types of the former class may be instanced the sweat of
mammals, and the slime of fish and many amphibians ; of the latter,
the secretion of the various modifications of sebaceous glands in
mammals ; of the uropygial gland of many birds ; and the fibre secre-
tions of the skins of certain fish {Myxine, Anguilla, etc.).

Such secretions are put to a variety of uses in the vertebrate series.
Of the first class, the sweat of the mammal is at once an excretion and
a means of regulating body temperature by evaporation, while the
slime of the frog or fish is protective in function. Of the second class,
the greasiness of the sebum of the mammal, or secretion of the tail
gland of the bird, protects skin, hair, or plumage from imbibition of
water ; the secretion of the Meibomian glands of the eyelids prevents
overflow of tears ; the viscosity of the ear wax interferes with the entrance
of foreign bodies into the auditory canal ; while, in special cases, volatile
substances of good or evil odour, contained in the secretion, may serve
the purposes of sexual attraction or protection from enemies.

In hairy mammals, it is only in certain cases, or on certain parts of the body,
that sweating is observed. Rabbits, rats, and mice are not known to sweat at
all, the dog sweats but little, the cat only on the hairless pads of the feet ;
while on the other hand the horse sweats profusely on all parts. The snouts
of pigs and oxen contain glands similar to sweat-glands, the secretion of which
keeps the part moist.

Instances of glands used for purposes of sexual attraction are — the glands of
the suborbital pit of many ruminants and some hogs, the cheek gland of the
elephant, the pectoral glands of certain tropical bats, the flank glands of shrews,
the sacral gland of the peccary, the groin glands of antelopes, the preputial glands
of the beaver and musk-deer, the anal glands of the hare, marsupials, armadillos,
two-toed sloth, otter, hysenas, and civets, and the glands at the base of the tail
of shrews and the fox. The anal glands of the skunk are used for protection.

The hoof gland of most bisulcate ungulates, opening in the cleft between
the tAvo divisions of the hoof, is probably of use in protecting the horny



670 SE CRE TION AND ABSORPTION B Y THE SKIN.

matter from imbibition of water ; in the one-horned rhinoceros a gland opens on
the posterior aspect of each foot.

The function of the curious gland at the back of the thigh of male
monotremes, supplying its secretion by a long duct to the hollow horny spur on
the heel (so like in arrangement to the poison gland and fang of a snake) is
not known with certainty.

There are glands in the skin of the male of the kangaroo, Halmaturns
rufus, which secrete a red substance adhering to the hair, while the maxillary
glands of the female dwarf antelope, Ce^haJolojjJms ijygmceus, secrete a blue
substance reddened by acid.^



Chemical Natuee of Skin Secretioxs.

(ft) "Watery secretions. — Naturally the composition of the sweat
of man and mammals has received more attention than that of other
skin secretions.

Since the quantity of sweat secreted is dependent upon so many
conditions, it is of little value to quote the numbers obtained hj
different observers, apart from a statement of the special conditions-
under which the observations took place.

There are several methods of collecting the sweat of the whole body,
or of special parts. Evaporation may be hindered by enclosing a part,
such as the forearm and hand, in a rubber bag, and the sweat collected
in a bottle tied into the lower end of the bag.^ The subject may sit in a
Pettenkofer and Voit's respiration chamber (but breathe through tubes
to the exterior), and the water given off by the skin be calculated from
the readings of hygrometers in the ingoing and outgoing currents of
air.^ Or the secretion of the skin may be stimulated by raising the
temperature of the surrounding air, while the whole body, with the
exception of the head, is enclosed in a convenient receptacle.* By
the hot-air method, Argutinsky ^ collected a quarter of a litre of sweat
in half an hour, at a temperature raised during the experihient from
27° to 41" C. Schierbeck,^ by the hygrometric method, calculated that
in his own case, when clothed and at rest, the air in contact with the
skin being at the normal temperature within clothing (32'' C), 2 or 3
litres of sweat were given off in twenty-four hours. ISTo calculations of
the total secretion of sweat can be made from local estimates, because the
richness of various districts of the skin in sweat-glands is very different.

In the body at rest the sweat is evaporated as fast as it is formed,
and it is only under conditions exciting the glands to increased action,
that the fluid collects upon the surface.

In the resting condition of the body the temperature of the
surrounding air must be raised to about 33° C. before the stimulus to^
increased activity of the sweat-glands is evoked.^

The following table is of interest as indicating that, at the time of

1 Weber, Arch. f. mikr. Anat., Bonn, 1888, Bd. xxxi. S. 499. For fmtlier information
on sucli glands, see Owen, ''Comparative Anatomy and Physiology of Vertehrata," London,
1868, vol. iii. p. 632 ; Leydig, Ztschr.f. ivissensch. ZooL, Leipzig, 1850, Bd. ii. S. 1 (anal
glands).

- Anselmino, Wagner's " Handworterbncli d. Physiol.," art. "Haut."

^Schierbeck, Arch. f. Physiol., Leipzig, 1893, S. 116.

■* Favre, Comjyt. rend. Acad. d. sc, Paris, 1852, tome xxxv. p. 721.

5 Arch.f. d. ges. Physiol., Bonn, 1890, Bd. xlvi. S. 594. '^ Loc. cit.

'' Schierbeck, loc. cit.



CHEMICAL NATURE OF SKIN SECRETIONS.



671



the breaking out of sweat, the excretion of carbon dioxide by the skin
is also suddenly increased, a fact probably related to the increaseil
activity of the giand-cells : —

Excretion of Water and Carhon Dioxide by tlie Skin at various Temperatures

of Surrounding Air.
(Separate experiments on same individual, naked, in a Pettenkofer and Voit's chamber).^



Temperature of
Chamber.



Water Excretion
(Grms. per Hour).



29°


•8C.


30"


■4 ,,


31°


■5 ,,


31°


•9 ,,


32°


■8 ,,


33°


■8 ,,


35°


•4 ,,


35°


■7 ,,


38°


■4 ,,



22-2

27-8

71-9

50-3

73-4

82-6

106-8

107-0

158-8



Water E.xcretion

(Grms. per Twentj'-

four Hours).



532-8
667-2
17-25 -6
1207-2
1761-6
1982-4
2563-2
2568-0
3811-2



Carbon Dioxide
(Grms. jjer Hour).



Carbon Dicxide

(Gnns. per Twent} -

four Hours).



•37
•40
•37
•35
•35
•87

1^04
-9

1-23



8-9

9-6

8-9

8^4

8-4

20-9

25-0

2] -6

29-5



The sweat of man is a colourless, opalescent liquid of salt taste,
poorest in solids of all the secretions, though richest in salts in relation
to organic solids.

Sweat is acid in reaction, even when collected from the palm of the
hand, where there is no danger of admixture of sebaceous secretion.-
This acidity is probably due to volatile fatty acids, w^hich may be
subsequently driven off, leaving an alkaline reaction at the surface of
the skin.^ In profuse sweating the acidity may give way to neutralit}%
followed later by alkalinity.*





In 1000 parts.


Favre.


Schottin.


Funke.






Water ....


995-573


977-40


988^40






Solids






4-427


22-60


11 •eo






Epithelium
Fat .






•013


4-20


2-49






Lactates






•317










Sudorates .






1^562










Extractives






•005


11-30








Urea .






•044




1^55






Sodic chloride






2^230


3-60








Potassic chloride




•024










Sodic phosphate




Traces


1-31








Alkaline sulphates




•Oil


-39








Earthy phosphates
Total salts .




Traces


7-00


4 -3 6




NOTI


: TO Table. — The sudoric or hidrotic acid


' Favre has n


Dt been found


by anv


subsequent observers. He gives the empirical formul
has not been found by any other observer.'


a, C,„H,cH.3(


D-^3. Lactic acid also



^ Schierbeck, loc. cit.

- Francois-Franck, "Diet, encycl. d. sc. med.," Paris, 1884, Ser. 3, tome xiii. p. 51,
Art. "Sueur."

STourton, "These de Lyon," 1879, No. 24, Ser. 1.

* Favre, loc. cit. ; Triimpy and Luchsinger, Arch. f. d. gcs. Physiol., Bonn, 1878,
Bd. xviii. S. 494.

■' For analysis of sweat of a rheumatic patient, see Harnack, Fortschr. cl. Med. , Berlin, 1 893,
S. 91 ; also Hermann, Jahresb. u. d. Fortschr. cl. Anat. u. Physiol., Leipzig, 1895. Bd. ii.
S. 226.



672 SECRETION AND ABSORPTION B Y THE SKIN

The specific gravity of human sweat is 1003 to 1006.

The table on p. 671, from Beaunis,^ gives the composition of sweat according
to Favre," Schottin,^ and Funke : ^ —

Relatively to the chlorides, the sulphates and phosphates of sweat are less
abundant than in urine. The following table is from Kast : ^ • —





Chlorides.


Phosphates.


Sulphates.


Sweat
Urine


1

1


•0015
•132


•009
■397



There is no doubt that urea is present in the svv^eat of man; the
variations in estimates of the amount by different observers being
probably caused by differences in the lapse of time between collection
and estimation, and consequent variations in the amount of trans-
formation into ammonium carbonate.

In two lots of sweat collected by the hot-air method, Argutinsky ^
found that 'SGS grm. urea was present in 225 c.c. of sweat collected in
half an hour, and '410 grm. urea in another sample of 330 c.c. collected
in three-quarters of an hour.

Of the total nitrogen excreted by the skin in one case, 6 8 "5 per



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 94 of 147)