_SECRETION AND COLLECTION OF VENOM IN SNAKES._
_Non-poisonous_ as well as _poisonous_ snakes possess _parotid_ and
_upper labial_ glands capable of secreting venom. In the former the
organs of inoculation are wanting, but we shall see later on that the
toxic secretion of their glands is just as indispensable to them as to
the snakes of the second category for the purpose of enabling them to
digest their prey.
For the morphological, histological, and physiological demonstration of
the existence of these glands in harmless reptiles we are indebted to
Leydig (1873), whose discovery has since been confirmed and extended
by the researches of Phisalix and Bertrand, Alcock, L. Rogers, and L.
Lannoy.
The parotids of Grass Snakes are mixed glands of the sero-mucous type.
The serous tubes are situate almost exclusively in the posterior
portion of the gland. As we proceed towards the anterior portion, we
find that these serous tubes are interspersed with others which are
exclusively mucous or sero-mucous, and they become entangled with those
of the upper labial gland, properly so-called. The substance of the
gland is divided into several lobes by bands of connective tissue;
the tubes are separated by _septa_ of the same tissue, in extremely
delicate layers (Lannoy).
In poisonous snakes these glands are much more developed, especially
in their hinder portions, which sometimes assume enormous dimensions.
They may attain the size of a large almond (_Crotalus_, _Naja_), and
they then occupy the spacious chamber already described (Chap. I., p.
10), which is situated behind the eye on each side of the skull.
Each gland is surrounded by a thick capsule of fibrous tissue, two
prolongations of which, the one anterior, the other posterior, keep it
in its place beneath the _masseter_ muscle. A portion of the latter
is inserted in the capsule itself, in such a way that when the snake
closes its jaws to bite, the gland is forcibly compressed and the
contained liquid is squeezed into its excretory duct.
Between the muscle and the envelope of the gland there is a serous
pouch, which enables the one to slide over the other.
The excretory duct runs along the outer side of the upper jaw,
and opens by a slit at the base of the poison-fang, with which it
inosculates at right angles in a little muscular mass forming a
_sphincter_.
In the normal position of repose, the poison-fang is always concealed
by a gingival fold of mucous membrane, in the substance of which are
buried a few fibres of the tendon of the internal pterygoid muscle.
When the latter contracts, the tooth is almost completely exposed, and
the efferent duct of the gland then assumes an oblique position, which
allows of the direct discharge of the venom through the canal which
runs along the greater portion of the length of the tooth.
When the poison-fangs are folded back in their sheath, the poisonous
secretion can escape freely into the buccal cavity by the slit situated
at the base of the fangs.
At the moment when the animal is about to bite, when it throws back its
head and opens its jaws, directing its fangs forwards, the muscles that
come into action (_masseters_, _temporals_, and _pterygoids_) compress
the glands on each side, and cause the venom to be expelled in a sudden
jet, as if by a sort of ejaculatory process. In the case of certain
species the venom may be projected to a distance of more than a yard.
The quantity of venom secreted by the glands varies greatly, according
to the length of time which has elapsed since the animal took its last
meal, and in accordance with a number of other conditions not very easy
to determine.
The Common Viper of Europe yields scarcely 10 centigrammes of poison,
while an adult Indian Cobra may excrete more than 1 gramme.
* * * * *
Freshly collected venom is a syrupy liquid, citron-yellow or slightly
opalescent white in colour.
When dried rapidly _in vacuo_ or in a desiccator over calcium chloride,
it concretes in cracked translucent lamellæ like albumin or gum arabic,
and thus assumes a crystalloid aspect. In this condition it may be kept
indefinitely, if protected from light, air, and moisture. It dissolves
again in water just as readily as albumin or dried serums.
I regularly weighed the dry residue from eleven bites made on a
watch-glass by two _Naja haje_, received at my laboratory from Egypt
at the same time, and placed in the same case. Both snakes were
approximately of equal length, 1,070 millimetres. Throughout the entire
course of the experiment, which lasted _one hundred and two days_,
neither of them took any food, but they drank water and frequently
bathed.
The results that I obtained are shown in the table on next page.
It will be seen that in one hundred and two days, an adult _Naja haje_
is capable of producing on an average 0·632 gramme of liquid venom,
equal to a mean weight of 0·188 gramme of dry extract; and we may
conclude that 1 gramme of _liquid_ gives 0·336 gramme of _dry_ venom.
In Australia it has been found by MacGarvie Smith, of Sydney, that
_Pseudechis porphyriacus_ yields at each bite a quantity of venom
varying from 0·100 gramme to 0·160 gramme (equal to 0·024 gramme to
0·046 gramme of dry venom), and that a _Hoplocephalus curtus_ (Tiger
Snake) yields 0·065 gramme to 0·150 gramme of liquid venom, with 0·017
gramme to 0·055 gramme of dry residue. In all the experiments of this
physiologist, the proportion of dry residue varied from 9 to 38 per
cent. of the liquid venom excreted by the reptile.
A _Lachesis lanceolatus_ (Fer-de-lance) from Martinique, of medium
size, when both of its glands were squeezed, furnished me with 0·320
gramme of liquid venom, and 0·127 gramme of dry extract.
+---------+----------+-------------------+-------------------+
| | | _NAJA HAJE_ I. | _NAJA HAJE_ II. |
|Number of| Date | WEIGHT OF VENOM | WEIGHT OF VENOM |
| bite | +---------+---------+---------+---------+
| | | Fresh | Dry | Fresh | Dry |
+---------+----------+---------+---------+---------+---------+
| | | Gramme | Gramme | Gramme | Gramme |
| 1 | April 20 | 0·119 | 0·031 | -- | -- |
| 2 | “ 23 | -- | -- | 0·151 | 0·043 |
| 3 | May 14 | 0·124 | 0·035 | -- | -- |
| 4 | “ 21 | -- | -- | 0·132 | 0·037 |
| 5 | “ 28 | -- | -- | 0·091 | 0·019 |
| 6 | June 2 | 0·127 | 0·039 | -- | -- |
| 7 | “ 19 | -- | -- | 0·121 | 0·043 |
| 8 | July 1 | -- | -- | 0·078 | 0·026 |
| 9 | “ 2 | 0·122 | 0·048 | -- | -- |
| 10 | “ 25 | -- | -- | 0·111 | 0·034 |
| 11 | “ 26 | 0·079 | 0·021 | -- | -- |
+---------+----------+---------+---------+---------+---------+
| | Totals | 0·581 | 0·174 | 0·684 | 0·202 |
+---------+----------+---------+---------+---------+---------+
Two large _Cerastes_ vipers, from Egypt, yielded me, one 0·123 gramme,
the other 0·085 gramme of liquid venom, which, after desiccation, left
respectively 0·027 gramme and 0·019 gramme of dry residue.
Under the same conditions, a magnificent _Crotalus confluentus_
(Mottled Rattle-Snake), for which I was indebted to the kindness of Mr.
Retlie, of New York, yielded, two months after reaching my laboratory,
0·370 gramme of liquid venom and 0·105 gramme of dry extract in _a
single bite_.
The total quantity of liquid venom that I found contained in the two
glands of the same reptile, when extirpated after death, and after the
snake had been in the laboratory for five months, amounted to 1·136
gramme, which gave 0·480 gramme of dry extract.
We see, therefore, that the proportion of dry residue, including
albumin, salts, the _débris_ of leucocytes, and the toxic substance,
oscillates between 20 and 38 per cent. Its strength varies with the
length of time that has elapsed since the snake’s last bite or last
meal.
* * * * *
From the _histological standpoint_, the process of the secretion of
venom, in the cells of the glands, may be divided into two stages:--
(_a_) A stage of nuclear elaboration.
(_b_) A stage of cytoplasmic elaboration.
These two stages are superposed and successive.
In addition to the passive exchanges between the nucleus and the
cytoplasm, the nuclear mass actively participates in the secretion.
This participation is rendered evident:--
(1) By the difference of chromaticity in the granules of chromatin.
(2) By the emission of formed granules into the cytoplasm, granules
which are spherical and of equal bulk, with the chromatic reactions of
differentiated intranuclear chromatin.
(3) By the exosmosis of the dissolved nuclear substance, accessorily
formed in an ergastoplasmic shape.
These formations constitute, on the one hand, the granules of
_venogen_; on the other, the ergastoplasmic venogen. In the poison-cell
of _Vipera aspis_, and in the serous cell of the parotid glands of
_Tropidonotus natrix_ (Grass Snake) the venogen is elaborated chiefly
in granular form.
On entering the perinuclear cytoplasm, the granule of venogen and the
ergastoplasmic venogen may either disappear immediately, as happens
in periods of cellular stimulation, or else continue to exist for
some time within the cell, indicating a period of saturation by the
elaborated material.
During cytoplasmic activity the granule of venogen and the
ergastoplasmic venogen disappear.
Nuclear elaboration and cytoplasmic elaboration constitute two
different cycles of secretion. The effect of the nuclear cycle is to
furnish the cytoplasm with the elements necessary for the work of
secretion properly so-called. Cytoplasmic elaboration is not confined
to the basal protoplasm, but takes place throughout the entire cell: it
is especially active in the perinuclear cytoplasm.
The granule of venogen is distinguished from the granule of elaborated
venom by its affinity for Unna’s blue, safranin, and fuchsin. The
granule of venom has an affinity for eosin; it is never excreted in
granular form, but after intracellular dissolution.
Venogen is never met with in the lumen of the gland-tube.[6]
COLLECTION OF VENOM.
Venom can be extracted from the poison-glands of either freshly killed
or living snakes.
In cases in which the venom of dead snakes has to be collected, the
best method of extraction consists in fixing the head of the animal to
a sheet of cork and carefully dissecting out the gland on each side.
The reptile being placed on its back, the lower jaw is removed with a
pair of scissors; two strong pins or two tacks are thrust through the
skull, in the median line, in order to keep the head from moving. The
poison-fangs are next drawn out of their sheaths, and, without injuring
them, the two poison-ducts, which open at their bases, are isolated and
tied with a thread in order to prevent the poison from running out.
The dissection of the glands is then very easy; they are lifted out
and placed in a saucer. The end of the duct is cut between the gland
and the ligature, and with a pair of fenestrated or polypus forceps the
whole of the glandular mass is gently squeezed from behind forwards,
the liquid which flows out being received in a large watch-glass.
If pressed for time, a more simple method of operating is to hold
the head of the snake in the left hand, with the mouth open and the
lower jaw directed downwards. A watch-glass, capsule, or receptacle of
some sort, such as a cup or plate, is then introduced by an assistant
between the jaws, and, with the index finger and thumb of the right
hand, the whole of the region occupied by the glands on each side of
the upper jaw is forcibly compressed from behind forwards; the poison
flows out by the fangs.
* * * * *
The extraction of the venom from living snakes is effected in the same
manner. The animal being firmly held by the neck, as close as possible
to the head, so that it cannot turn and bite; it can be made to eject
the greater portion of the liquid contained in its two glands by
compressing the latter with force from behind forwards, as one would
squeeze out the juice from a quarter of an orange (fig. 85).
It is necessary to take care that the reptile cannot coil itself round
furniture or other objects in the vicinity of the operator, for if
this should happen there would be the greatest difficulty in making it
let go, especially if dealing with a strong animal such as a Cobra,
Rattle-Snake, or Fer-de-lance.
Snakes of the last-mentioned kind are especially difficult to manage.
In order to avoid the risk of being bitten, it is always wise to
begin by pinning down the head of the animal in a corner of its cage
by means of a stick, and to seize it with a pair of long fenestrated
tongs shaped like forceps. The operator then easily draws the reptile
towards him and grasps it firmly by the neck with his left hand, always
as close to the head as possible, at the same time raising the body
quickly in order to prevent it from taking of anything. In this way
the most powerful snake is perfectly under control.
[Illustration: FIG. 85.--COLLECTING VENOM FROM A
_Lachesis_ AT THE SEROTHERAPEUTIC INSTITUTE AT SÃO PAULO
(BRAZIL).]
[Illustration: FIG. 86.--CHLOROFORMING A COBRA IN ORDER TO
COLLECT VENOM, AT THE FRENCH SETTLEMENT OF PONDICHERRY, IN INDIA
(STAGE I.).]
At Pondicherry, where is collected the greater portion of the venom of
_Naja tripudians_ used by me for the vaccination of the horses that
produce antivenomous serum, it is customary to chloroform the snakes in
order to render them easier to manipulate.
The reptile is placed in a large covered jar, containing a pad of
absorbent wool impregnated with chloroform (figs. 86, 87), and in a few
minutes it is stupefied. It is then grasped by the neck with the hands,
and the edge of a plate is slipped between its jaws. On compressing the
two poison-glands with the fingers, the venom dribbles out on to the
plate.
A detailed description of this technique will be found in a note kindly
drawn up for me by my friend Dr. Gouzien, late head of the Medical
Staff of the French Settlements in India, and reproduced further on in
the section of this book devoted to documents. The note in question was
accompanied by figs. 17, 18, 19, 86, 87, and 88, which are reproduced
from photographs, for which I am indebted to the kindness of M.
Geracki, Engineer of the Savanna Spinning Mill at Pondicherry, Dr.
Lhomme, and M. Serph, Assistant Surgeon-Dispenser.
The collection of the venom having been completed, the snake is put
back into its cage again, the tail and the body being introduced first,
and then the head. The lid or trap-door is half closed with the left
hand, and, with a quick forward thrust, the right hand releases its
grasp of the reptile and is immediately withdrawn; at the same time the
left hand completes the closure of the cage. The snake is temporarily
dazed, as though stunned, and it is only after the lapse of a moment
that it thinks of darting open-mouthed at the walls of its prison.
When it is desired to procure large quantities of venom, as is
indispensable in laboratories where antivenomous serum is prepared,
the endeavour must be made to keep the snakes alive for the longest
possible time. It then becomes necessary to resort artificial feeding
in the manner previously described (see p. 17), for they very often
refuse to feed themselves.
[Illustration: FIG. 87.--CHLOROFORMING A COBRA IN ORDER TO
COLLECT VENOM, AT THE FRENCH SETTLEMENT OF PONDICHERRY, IN INDIA
(STAGE II.).]
Except when a snake is _moulting_, the venom can be extracted from its
glands about every fortnight; and it is better that the extraction be
not performed concurrently with artificial feeding, since, owing to the
fact that the venom serves the animal as digestive juice, the reptile
will soon perish if deprived of the means of digesting the food that it
is obliged to receive. It is best, therefore, to select one day of the
week for artificial feeding, and the corresponding day of the following
week for the extraction of the venom.
When the venom has been collected, it must immediately be in a
desiccator over calcium chloride or sulphuric acid, in order to dry
it rapidly. In hot countries, and where no laboratory specially
equipped for the purpose exists, it will suffice to dry the venom in
a current of air, or even in the sun. It then concretes in scales of
a citrin colour, more or less dark, according to the concentration
of the liquid. In this dry condition, placed in well-corked bottles,
protected from damp air, it may be kept almost indefinitely without
losing anything of its original toxic power. On the contrary, if the
desiccation be imperfect it undergoes a somewhat rapid change, and
assumes a disagreeable odour of meat peptone. I have kept samples of
various venoms, dried as described, for _fifteen_ years without any
sensible diminution of their activity.
[Illustration: FIG. 88.--COLLECTING COBRA VENOM AT PONDICHERRY
(STAGE III.).]