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cent, was present in urea, and 31 "5 per cent, in ammonia; while in the
other the numbers given are 74'9 per cent, of total nitrogen in urea, and
25 '1 per cent, in ammonia.

The same observer, by taking severe walking exercise in a special
suit of clothes, which was extracted at the end of the period of
work, and the extract analysed by the Kjeldahl method, obtained results
as follows : —

Work. Mgrms. of Nitrogen

excreted by the Skin.
20 to 22 kilometres in seven hours (July) ..." 704-4
18 to 20 „ with ascent of ISOO^metres (August) . 753-5

1600 metres (October) 219*3

The nitrogen excreted by the skin may amount to 4-7 per cent,
•of that by the urine, and hence may have to be taken into account in
some experiments on nitrogenous metabolism.

In ursemic conditions, the excretion of urea by the skin is greatly
increased, so much so, in some cases, that crystals of urea have been
found on the skin.'^

According to Capranica,^ creatinine to the extent of -04 per cent,
is present in human sweat. The small amounts of fatty acids are made
up of formic, acetic, butyric, propionic, and caproic acids. Ethereal
sulphates of phenyl and skatoxyl are present in small amount, the
proportion of ethereal to inorganic sulphates l)eing, according to Kast,^



190.



^ " Nouveaux elements de physiologie humaine," Paris, 1888, 3rd edition, tome ii. p.
).

- Loc. cit.

^ " De Sudore," Diss., Leipzig, 18.51.

•^ Untcrsuch. z. Naturl. d. Menscli. n. d. Tliierc, 1858, Bd. iv. S. 36.
^ Ztschr. f. physiol. Cham., Strassburg, 1887, Bd. xi. S. 501. '^ Loc. cit.

' Schottin, loc. cit.
* Arch. ital. dehloL. Turin, 18S2, tome ii. '■' Loc. cit.



CHEMICAL NATURE OF SKIN SECRETIONS.



673



1 to 12. Indigo is sometimes developed in sweat/ though whether from
indoxyl secreted, or as the result of the growth of chromogenic
micro-organisms, is not certain.

The sweat of the horse has been studied by Leclerc ^ and Fred Smith.^
This secretion normally contains proteids, a fact which may partly accoimt for
the debilitating effects of profuse sweating in horses.



Percentage Composition of Sweat of Horse {Fred Smith).



Alkaline,


sp. gr. 1020 ; Watei


, 94-


3776


; Organic solids


5-0936.






Serum albumin . . . . '1049




Serum globulin








■3273




Fat .








■0020




Chlorine .








•3300




Lime








■0940




Magnesia .








•2195




Phosphoric acid
Sulphuric acid
Soda








Trace
Trace
•8265




Potash .








1-2135



•5288 ; Ash,



Both Leclerc and Smith found urea in the sweat of the horse.

The sweat of the hippopotamus contains a reddish-brown pigment not yet
identified.'^

Buisine^ has investigated the constituents of that part of the "sweat" of
sheep which is soluble in water. He foimd potash soaps of the fatty acids
from acetic to capric ; urea and ammonium carbonate ; potash salts of malic,
glycolic, pyrotartaric, oxalic, succinic, lactic, hippuric, benzoic, and uric acids ;
phenylsulphate of potassium, and traces of leucine and tyrosine. Malic acid
Avas previously only known as a vegetable product.

Of the watery secretion of the skin of amphibians little is known. The
reaction of the secretion of the " mucous glands " is alkaline, while that of
the " granular glands," ^ chiefly found on the dorsal surface of the flanks
and legs, is acid. According to Leydig,'^ acrid substances are secreted in
addition to mucin, in the case of the tree frog. In the case of the salamander
and toad, poisonous substances have been separated.^

Gratiolet and Cloez ^ state that the poisonous substance in the skin glands of
the toad and salamander is soluble in alcohol and of the nature of an alkaloid.
Yulpian ^^ and more recently Phisalix and Bertrand ^^ have investigated this
substance in the case of the toad. The symptoms of poisoning are — paralysis

^ Bizio, Sitzungsh. d. k. AJcacl. d. JFissensch. , Wien, Bd. xxxix. S. 33 ; Hofmann,
Wie7i. med. TFch^ischr., 1873, S. 292 ; Bergmanu, St. Fetersh. med. Ztsclir., 1868,
Bd. xiv. S. 28.

~ Compt. rend. Acad. d. sc, Paris, 1888, tome cvii. p. 123.

^ Journ. Physiol., Cambridge and London, 1890, vol. xi. p. 497.

■^ Weber, "Stud. it. Saiigethiere," Jena, 1886, S. 9.

^ Compt. rend. Acad. d. sc, Paris, 1886, tome ciii. p. 66; 1887, tome civ. p. 1292;
and 1888, tome cvi. p. 1426.

^Hermann, Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 291.

'^ Arch. f. mikr. Anat., Bonn, 1875, Bd. xii. S. 119; und Biol. Centralbl., Erlangen,
1892, Bd. xii. S. 458.

^ Zalesky, Roppe-Seyler's Med.-chem. Untersuch. , Berlin, 1866, Bd. i. S. 85; Casali,
Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 1873, S. 64 ; Foruara, ibid.,
1877, S. 74.

** Compt. rend. Acad. d. sc, Paris, 1852, tome xxxiv. p. 729.

^° Compt. rend. Soc de bid., Paris, 1854, p. 135.

^1 Arch, de physiol. norm, at path., Paris, 1893, Ser. 5, tome v. p. 511.

VOL. I.— 43



674



SECRETION AND ABSORPTION BY THE SKIN.



commencing in the liind-limbs, slowing and final arrest of the heart, and
constriction of the pupil. Frogs, guinea-pigs, and small birds are killed by
injection of the alcoholic extract of the collection of glands forming the
so-called " parotids " of the toad. The poisonous substance is dialysable,
and is probably an alkaloid. The blood of toads also contains small amounts
of this substance, and the serum of a toad will kill a frog if introduced into
the dorsal lymph sac.

The slime of fish is secreted by goblet cells in the epidermis, but has been
little investigated from the chemical standpoint, on account of the great
difficulty in obtaining it in sufficient quantities, and free from foreign
substances. The slime of Myxine glutinosa is most easily obtained, and is
found to contain a mucin-like body, which, however, does not yield a
reducing sugar on boiling with dilute acid.^

The reaction of the skin of the eel and of Myxine is alkaline to litmus,
but curiously does not affect phenophthalein. A reducing sugar can be
obtained from the slime of the eel by boiling Avith dilute acid.- According
to Alcock,^ the slime of the Ammocmte larva yields a proteolytic ferment on
extraction.

(h) Sebaceous secretions. — Such secretions are formed by prolifera-
tion and subsequent degeneration of the cells lining the sebaceous
glands, in which karyokinetic figures are frequent.^

These glands are present over the whole surface of the body, with the
exception of the palms of the hands, soles of the feet, dorsal surface of the
third phalanges, and gians penis.

Since it is impossible to collect sufficient quantities of the sebum of
man for analysis, we have to rest content with analyses of the contents
of sebaceous cysts, the vernix caseosa of the fcetus, or the contents of
dermoid cysts of the ovary.

Glycerin and cholesterin fats, fatty acids, albumin (casein ?), free
cholesterin and isocholesterin, with water and salts, are the main con-
stituents of sebum.

The following table is taken from Hoppe-Seyler : ^ —





Contents of a
Distended
Sebaceous

Gland in Man.


Vernix Caseosa
of Man.


Smegma
Preputii
of Man.


Smegma
Preputii
of Horse.


Water


317-0


669-8






Epithelium and albumin


617-5


40-0


56-0




Fat


41-6


475-0


528-0


499-0


Fatty acids ....


12-1








Alcoholic extract .




150-0


74-0


96-9


Water extract




33-0


61-0


54-0


Ash .....


11-8









^ Journ. Physiol., Cambridge and London, 1893, vol. xv. p. 488.

^Reid, Phil. Trans., London, 1894, vol. clxxxv. p. 319.

» Proc. Phil. Soc, Cambridge, 1891, vol. vii. pt. 5, p. 252.

■^Bizzozero and Vasale, Med. CInr- Ccntralhl., Wien, 1884, S. 77 and 179.

"Physiol. Chem.," Berlin, 1881, Tli. 4, S. 761.



CHE MIC A L NA TURE OE SKIN SE CR E TIONS. 6 7 5

Sotnitschewsky/ in an analysis of a dermoid cyst of the ovary, found
tripalmitin, tristearin, and triolein ; soaps of the acids of these fats and
of caproic and caprylic acids, albumin, cholesterin, and an alcohol of
high molecular weight, which, however, was not cetyl alcohol.''^ Tyrosine,
hypoxanthin, xanthin, sugar, and glycogen were aljsent.

The vernix caseosa of man, according to Euppel ^ and Liebreich,'^ con-
tains cholesterin fats of oleic and palmitic acids, as well as glycerin fats,
and also free cholesterin and isocholesterin.

The cerumen of the ear has been investigated by Petrequin,^ and is
found to contain potash soaps of oleic and stearic acids in the case of man
and the ox, while in the dog the base is lime, and in the horse magnesia.

Wool fat, the sebaceous secretion of the sheep's skin, was proved by
Hartmann ^ to contain no glycerin fats, but only those with cholesterin
as alcohol. Schulze and Urich^ confirmed this, and also found free
cholesterin and isocholesterin.

These cholesterin fats (so-called " lanoline ") have been specially
investigated by Liebreich,^ who finds that they are associated with
keratinised structures, and are not necessarily formed in sebaceous
glands, but may be formed within epidermic cells. Tortoiseshell, whale-
bone, horn, quills of porcupine and hedgehog, hoof of horse, and beak of
crow, all contain these fats. The skin of the two-toed sloth has no sebace-
ous glands, and yet contains cholesterin fats, while pigeons bereft of
their uropygial glands still have these substances in their feathers.

Such fats are peculiar, in that they can take up more than their weight
of water, and also in that they do not become rancid, and offer a
complete protection against the entrance of micro-organisms. Liebreich
compares them to the wax of plants, which is an ether of a monohydric
alcohol with a fatty acid.^

The secretion of the tail gland of the bird ^^ has been cliemieany investi-
gated by de Jonge.^^

The secretion contains cetyl alcohol, the alcohol of spermaceti. K'o sugar
or urea is present. Geese deprived of the tail gland and immersed in water are
found to take up from two to two-and-a-half times as much water in their
plumage as normal birds. ^^

The so-called " pigeons' milk," with which the young birds are fed by both
parents during the earlier days of life, is practically a sebaceous secretion of
temporary glands formed in the lateral pouches of the crop in both cock and

1 Ztschr. f. physiol. Chem., Straasburg, 1880, Bd. iv. S. 345.

" Ernst Liidwig {Ztsclir. f. physioL Ghem., Strassburg, 1897, Bd. xxiii. S. 38) lias quite
recently found cetyl alcohol in the contents of dermoid cysts of the ovary.

3 JMcL, 1895, Bd. xxi. S. 122.

4 "Verhandl. d. BerL physiol. Gesellsch.," in ^rc/i. /. Physiol, Leipzig, 1890, S. 363.
^Gompt. rend. Acad. d. sc, Paris, 1869, tome Ixix. p. 987; also 1869, tome Ixviii.

p. 940; Jahresb. il. d. Fortschr. d. Thier-Ghem., "Wiesbaden, 1871, Bd. i. S. 36; 1874,
Bd. ii. S. 33.

" Inaug. Diss., Gottingen, 1868.

7 £er. d. deutsch. chem. Gesellsch., Berlin, 1872, Bd. v. S. 1075 ; 1874, Bd. vii. S. 570.

8 Berl. Mill. TVchnschr., 1885, Bd. xlvii. S. 761 ; Gompt. rend. Acad. d. sc, Paris, 1888,
tome cvi. p. 1176 ; and "Verhandl. d. Berl. physiol. Gesellsch.," in Arch. f. Physiol.,
Leipzig, 1890, S. 363.

" The secretion of the HarJerian gland of the orbit of rodents, though fatty in nature, is
not formed by disintegration of cells ; Wendt, ''tjeber die Harder'sche Drhse," Strassburg,
1877 ; Kamocki, Biol. Gentralhl., Erlangen, Bd. ii. S. 709.

1° For anatomy, see Robby Kossmann, Ztschr. f. wissensch. Zool., Leipzig, 1871, Bd.
xxi. S. 568.

" Ztschr. f. physiol. Ghem., Strassburg, Bd. iii. S. 225.

12 Max Joseph, Arch. f. Physiol. Leipzig, 1891, S. 81.



676 SE CRE TION AND ABSORPTION B V THE SKIN.

hen. It contains fat, a proteid clotting with rennet, glohulin, salts, and water,
but is free from sugar. ^

The secretion of the leg glands of lizards is probably of sebaceous nature.^
In certain fish, in addition to the secretion of slime by the goblet cells of
the epidermis, a formation of fibrils takes place from specialised cells, termed
" club cells," which may be distributed in the general epidermis or located in
special glandular involutions, as in the Myxinoid fishes. This secretion reaches
its highest development in the Myxinoids, and accounts for the extraordinarily
tenacious slime of this class. The process has, however, also been observed in
the case of the eel and lamprey.^

Mechanism of the Secketion of Sweat.

Goltz * in 1875 discovered the fundamental fact that excitation of
the peripheral end of the divided sciatic causes the appearance of beads
of sweat on the hairless pads of the hind-foot of the cat. He also sa\v
the same effect in a dog. In the next year, Ostroumow,^ and Kendall
and Luchsinger ^ confirmed the result, and extended the details of the
experiment.

Ostroumow showed that excitation of the abdominal sympathetic
cord produced the same effect ; that even after ligature of the aorta, sweat
was still secreted upon excitation of the appropriate nerves ; and, finally,
that injection of atropine completely annulled the effect of such excita-
tion.

Kendall and Luchsinger obtained the effect upon the fore-leg of the
cat and dog, by exciting the nerves of the brachial plexus, confirmed
the fact of the persistence of secretion after occlusion of the aorta, or
crural artery in the case of the hind-limb, and further showed that, even
after amputation of the leg, sweat could be produced on the pads of the
foot for some fifteen to twenty minutes, by stimulation of the sciatic.

The fact that the production of sweat is an act of true secretion,
and the existence of sudorific fibres having been demonstrated, the
course of the fibres from the spinal cord next engaged attention.

The existence of sweat-fibres for the lower limb in the abdominal
sympathetic cord, demonstrated by Ostroumow, was confirmed by
Luchsinger '^ and Nawrocki,^ and extended by both the latter observers ^
to the thoracic sympathetic cord, for the fore-limb. Later, sudorific
fibres for the face, running in the cervical sympathetic, were demon-

^ John Hunter, " Observations on Certain Parts of the Animal CEconomy," London, 1786,
p. 191 ; Hasse, Ztschr. f. rat. Med., 1865, Reihe 3, Bd. xxiii. ; Claude Bernard, " Les
iiquides de I'organisme," Paris, 1859, tome ii. p. 232 ; Teichmanu, Arch. f. mikr. Anat.,
Bonn, 1889, Bd. xxxiv. S. 225 ; Charbonnel-Salle et Phisalix, Compt. rend. Acad. d. sc,
Paris, 1886, tome ciii. p. 286 ; Phisalix, Gompt. rend. Soc. de Mol., Paris, 1890, Ser. 9, tome
ii. p. 368 ; Reid, Rep. Brit. Ass. Adv. Sc, London, 1894, p. 812.

^ Leydit?, "Die in Deutschland lebenden Arteu der Saurier," 1872 ; Batelli, ^Irch. f.
mikr. Anat., Bonn, 1879, Bd. xvii. S. 346.

^ J. Miiller, "Untersuch. ii. die Eingeweide der Fische," Berlin, 1845, S. 11 ; Kolliker,
Wurzb. med. Zt>iclir., 1860, Bd. i. S. 1 ; F. E. Schulze, Arch. f. mikr. Anat., Bonn, 1867,
Bd. iii. S. 137 ; Frettinger, Bnll. Acad. roy. d. sc. de Belg., Bruxelles, 1876, St5r. 2, tome
xli. p. 599 ; Blomfield, Quart. Journ. Micr. Sc, Loudon, 1882, vol. xxii. p. 355 ; Reid,
Phil. Trans., London, 1894, vol. clxxxv. p. 319.

■* Arch. f. d. ges. Physiol., Bonn, 1875, Bd. xi. S. 71.

•^ Ref. in Jahresh. ii. d. Fortschr. d. Anat. u. Physiol., Leipzig, 1877, Bd. v.

« Arch./, d. ges. Physiol., Bonn, 1876, Bd. xiii. S. 212.

''Ibid., Bonn, 1877, Bd. xiv. S. 369.

* Gentralhl. f. d. med. Wissensch., Wien, 1878, S. 2.

" Nawrocki, Centralbl. f, d. vied. Wissensch., Berlin, 1878, S. 17 ; Luchsinger, ibid..
1878, S. 36.



THE SE CRE TION OF S WE A T. 677

strated by Liichsinger ^ and Nawrocki,^ in the horse and yjig by the
former observer, and in the pig by the latter. Both agreed that the
fibres reach the sweat-glands of the face by the infra-orbital branch of
the fifth cranial nerve, the junction being effected by branches from the
cavernous plexus of the sympathetic. Neither of these investigators
could satisfy himself of the presence of sweat-fibres in the facial nerve.

The origin of the sudorific fibres in the spinal cord has been studied
by Luchsinger, Nawrocki, Vulpian, Ott,^ and more recently by Langley.^

In the case of the hind-limb of the cat, according to Langley, the
sudorific fibres enter the sympathetic cord by the white rami coimmini-
cantes of the last two thoracic and first three or four lumbar nerves,
become connected with nerve-cells in the sixth and seventh lumbar, and
first and second sacral ganglia of the sympathetic, and leave by the
grey rami of these 'ganglia, to enter the anterior divisions of the corre-
sponding spinal nerves, and so the sciatic. The first and second lumbar
spinal nerves seem to supply the greatest number of secretory fibres.
The grey ramus to the sixth lumbar nerve is found to chiefly supply the
sweat-glands of the inner part of the foot, that to the second sacral
nerve the outer part, and, in the main, the successive rami from above
downward supply strips of the skin of the foot from within outwards,
though considerable, and, in different individuals, varied overlapping of
fields is noted.

In the case of the fore-limb, the same observer finds that the sweat-
nerves are supplied to the sympathetic chain by the fourth to the ninth
thoracic spinal nerves, the main outflow of fibres being usually found in
a nerve near the middle of the series. All these fibres run up in the
sympathetic cord to the ganglion stellatum, where a connection with nerve-
cells is effected, and by the grey rami of this ganglion reach the brachial
plexus,^ and so the median and ulnar nerves for their final distribution.

The grey rami to the sixth and seventh cervical nerves seem to chiefly
supply the inner part of the fore-foot, while that to the first thoracic
nerve chiefly supplies the outer part.

The fibres for the face, according to Nawrocki, leave the cord by the
second, third, and fourth anterior roots, and run up in the cervical sym-
pathetic to finally reach the infra-orbital branch of the fifth cranial
nerve, vid the cavernous plexus.

Yulpian ^ and Ott '^ maintained that, in addition to the sudorific fibres
supplied to the limbs vid the sympathetic, others are supplied directly from
the cord with the nerves forming the limb plexuses. The existence of such
fibres was denied by Nawrocki, and Langley fully confirms the statements of
this observer.

Furthermore, Yulpian and Ott maintained that inhibitory fibres to the
sweat-glands exist, and the theory has been recently revived by Arloing.^

Yulpian's evidence for the existence of such fibres was, that contem-

1 Arch.f. d. ges. Physiol., Bonn, 1880, Bd. xxii. S. 126.

" Gentralbl. f. d. mcd. Wissensch., Berlin, 1880, S. 945.

^ Compt. rend. Acad. d. sc, Paris, 1878, tome Ixxxvi. pp. 1308 and 1434 ; Ott, Journ.
Physiol., Cambridge and London, 1879, vol. ii. p. 42.

■^ Ihid., 1891, vol. xii. p. 347 ; ibid., 1894, vol. xvii. p. 296.

^ Eckhard {Arch. f. Anat., Physiol, u. wissensch. Med., Berlin, 1849, S. 427) quotes a
case in man Avhere contusion of the brachial plexus led to continuous sweating of the hand
on the side of the injury.

^ Loc. cit. ' Loc. cit.

^ Arch, dtphysiol. norm, etpatk., Paris, 1890, S^r. 5, tome ii. p. 1 ; and 1891, S^r. 5,
tome iii. p. 241.



678 SECRETION AND ABSORPTION B Y THE SKIN

poraneoTis excitation of cut sciatic and abdominal sympathetic causes less sweat
on the pads of a cat's feet than excitation of sciatic alone, and the sweat-
stimulating drug pilocarpine causes more sweating when sciatic or sympathetic
are cut than intact.

Later, Yulpian ^ abandoned this theory. He was led to the idea of the
existence of inhibitory fibres in the cervical sympathetic by consideration of
the old experiment of Dupuy," in which section of the cervical sympathetic
in the horse leads to sweating on the face on the side of section. Mere excess
of blood supply to sweat-glands, from the vaso-dilation which occurs simul-
taneously, is probably ^er se no stimulus to the action,^ but there is no doubt
that the excitability of the glands is thereby raised, and if, with Luchsinger,"^
it is admitted that a few sweat-fibres originate with the fifth cranial nerve, the
result is simply due to painful reflex, for Luchsinger got no sweating on section
of the sympathetic in the neck of a chloralised horse, though stimulation of
the peripheral end gave abundance.

The evidence adduced by Ott is the immediate cessation of a secretion pre-
viously evoked by pilocarpine, on excitation of the peripheral end of the
divided sciatic. Even if it were admissible that the accompanying vasomotor
constriction could cause the efi"ect (which it is not, seeing that in the ampu-
tated foot sweat can still be called forth), the result, he maintains, is obtained
too suddenly to be accounted for in this manner.

Again, he states that irritation of the abdominal sympathetic causes a
drjTiess of the pads of the foot on the side of irritation, and that pilocarpine
accentuates the difference in condition between the foot on the side of irrita-
tion and the normal foot on the opposite side.

Finally, division of the abdominal sympathetic produces moist pads on the
side of section, and injection of pilocarpine makes these pads sweat before the
others.

In Arloing's experiments on oxen and donkeys, the cervical sympathetic is
di^dded, and time is allowed to elapse until the vaso-dilation has passed off.
Pilocarpine now produces more marked secretion on the side of section, which
is interpreted as meaning that inhibitory impulses, restraining the action of the
glands on the sound side, have been removed on the side of section.

It has always been a matter of difficulty to differentiate the action of two
oppositely acting sets of fibres running in the same nerve-trunk, and it must
be admitted that the eWdence so far for the existence of inhibitory fibres for
sweat secretion is not strong.

Excitation by ax^prox^riate stimuli of the regions of the spinal cord
from which the sweat-fibres emerge leads to an outpoming of sweat on
the parts of the skin sux^XJlied by these filjres. Thus, if the spinal cord
is divided above the exit of the twelfth thoracic nerve in the cat, and
the animal exposed to heat (60° to 70' C. for five to ten minutes), sweating
still occurs on the hind-limbs.^

Xawrocki ^ and Marrne '^ denied this effect, and maintained that it
is only when there is continuity of the cord with the IjuIIj that such
stimulation causes sweating. Later, however, Nawrocki ^ obtained the

^ Viilpian et Pi,aymond, Comxit. rend. AccuL d. sc, Paris, 1879, tome Ixxxix. p. 11 ;
Itev. inf.eriwi. d.. sc. hiol., Paris, 1880, p. 115; and " Lecons sur les substances tox. et
mddic," tome i. pp. 148-149.

- Jov.rn. dernid., chir., pharrn., etc., Paris, 1816, tome xxxvii.

^ But see Levy, " Verhandl. d. Beri. pliysiol. Gesellsch.," in Arch. f. Physiol., Leipzig,
1892, S. 155.

■* Tagehl. d. Versaraml. deutsch. Natwrf. In Baden-Baden, 1879.

^ Lucksinger, loc. cit. *' Centralbl. f. d. med. Wissensch., Wien, 1878, S. 17.

'' 'Nachr. V. d. k. Gesellsch. d. Wissensch. u. d. Georg.-Aug. Univ., Gottingen, 1878,
p. 102.

^ Cenlralhl. f. d.. rwid,. JFissensch., Beriiu, 1878, S. 721.



THE SECRETION OE SWEAT. 679

result in a few cases with divided cord. Obviously a positive case in
such an experiment is worth many negative, since the excitability of
the cord below the section may possibly be depressed at the time of
making the test. It is generally accepted that spinal " sweat-centres "
exist.

On the other hand, no cerebral centres for sweating have yet been
experimentally demonstrated.^

According to Levy Dorn,^ the spinal " sweat-centres " are very re-
sistant to the action of cold. In cats cooled till the rectal temperature
was 22" to 28° C, sweating was still obtained by reflex excitation or
dyspnoea, but heating (70° C.) caused little sweating, the cooled cat
being as it were " protected," in that the heat which is to restore it,
does not, when applied, immediately call forth a reflex outpouring of
sweat, by the subsequent evaporation of which, heat would be abstracted
from the body.

The nervous mechanism of sweat secretion may be called into action
by central stimuli, by reflex action, or by peripheral stimuli. A venous
condition of the blood is one of the most active stimuli to the central
mechanism, and one frequently employed in experimental work. If an
animal be partially asphyxiated, after section of the spinal cord in the
mid-dorsal region, sweat breaks out on the pads of the hind-feet, even
after division of all the posterior roots behind the section.^

Eaising the temperature of the blood produces a similar effect, and
the result is also obtained with divided posterior roots, and hence is not



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