Report of the Royal Commission on the practice of subjecting live animals to experiments for scientific purposes : with minutes of evidence and appendix.

  • Great Britain. Royal Commission on Vivisection
Date:
1876
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Licence: Public Domain Mark

Credit: Report of the Royal Commission on the practice of subjecting live animals to experiments for scientific purposes : with minutes of evidence and appendix. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    App. IV. deeper nerves, it is well, in order to avoid confusion, to remove the descendens noni; the next step is to draw the larynx well to the side opposite to that chosen for the incision, so as to widen the space between it and the carotid artery. This done, the exposure of the superior laryngeal becomes easy. Its exact position is indicated in the figure ; its course is much twisted so as to allow of the up-and- down movements of the larynx. In preparing it, no cutting instruments must be used. It must be freed from the surrounding structures with the aid of two pairs of forceps, any veins in the way having been divided between two ligatures. Care must be taken, however, to leave a certain quantity of cellular tissue about it to serve as a kind of protective sheath, and make it somewhat less liable to get dry. The nerve having been prepared, a ligature must be tied round it as near as possible to the thyrohyoid membrane, after which it must be divided beyond. In the dog or cat the mode of preparation is very much the same as in the rabbit. In the cat, the comparative thickness of the nerve facilitates the manipulation. In exciting the superior laryngeal, the great source of difficulty is the proximity of the vagus and the consequent liability of that nerve to he acted on by the induced current in a unipolar way. This accident which is of course fatal to the success of the investigation, the functions of the two nerves being opposite, is to be avoided, not by the use of complicated arrangements for the insulation of the nerve, hut by placing it in such a way on the ordinary copper points that the part acted on is separated by a considerable air space from the surrounding tissues. Before beginning the excitation, the secondary coil must be shifted to a distance from the primary, and the primary current divided by means of Helmholtz’s side wire into two branches, one of which only passes through the breaker. The other is led directly from the battery to the coil, so that the primary current is never entirely opened. In this way the opening induction shock, which, in the ordinary arrangement of the induction apparatus, possesses a much greater tension than that of the closing shock, is so reduced that the two become nearly equal to each other.* Consequently, as the risk of unipolar action varies with the maximum intensity of the current, it is very much diminished by this contrivance, so much so, indeed, that if care is taken to prepare the nerve ])roperly, even moderately strong currents may be used without any effects referable to unipolar excitation of the vagus manifesting themselves. Excitation of the central end of the superior laryngeal produces, according to the strength of the current used, either diminution of frequency of the respiratory movements or complete relaxation of the muscles of inspiration. The most advantageous way of judging of its effect on the diaphragm, is to expose that muscle in the way directed in § 91. It is there seen that that muscle becomes absolutely llaccid during excitation of the nerve, and it is drawn up by the elastic contraction of the lungs, so as to assume its highest possible ])osition. When the excication is discon- tinued, the relaxation either gives way to natural breathing or is immediately succeeded by one or two vigorous inspira- tions. If the current is so feeble that it merely diminishes the frequency of the respirations, without arresting them, the tracings show that there is no diminution of the duration of the inspiratory acts, and that the slowing is entirely due to a prolongation of the interv^als, i.e., of the periods during which the diaphragm remains in the position assumed by it at the close of ordinary expiration. To record the effects graphically, any of the methods recom- mended in the preceding paragraphs may be used. If the method described in § 9.0 is employed, a tracing is obtained which exactly resembles fig. 255. The tracing fig. 2561 was drawn by inserting a bag between the diaphragm and the liver. Page 316.—The experiment by which it is proved that the respiratory phases of arterial pressure and pulse frequency are independent of the thoracic movement consists in curarizing a dog by the injection into tke venous system of a dose of solution of curare only just sufficient to paralyse the respiratory muscles. Page 319.—For this purpose a cannula must be fixed air-tight in the trachea. ..... Excessive respiratory movements in which at first the expansive efforts of the thoracic muscles, afterwards the expulsive efforts of the muscles of the abdominal wall are most violent. ...... * For a fuller explanation of the difTerence between the two indueed currents and of the effect of Helmholtz’s modification, see Rosenthal, “ Electrioitatslehre,” p. 120. t The tracing fig. 256, shows that during the whole period of excitation the diaphrs^m remained motionless in the position of cxpir.ation, with the exception that at gradu.ally lengthening intervals it executed momentary contractions. When after the cessation of excitation the respiratory movements were resumed, they were slower but more extensive than before. Towards the close of the first minute the animal becomes convulsed. These convulsions must be attentively studied, because they are the type by comparison with which all other convulsions of the same order are described or defined. . . . . _ Afterwards the contractions of the proper expiratory muscles are accompanied by more or less irregular spasms of the muscles of the limbs, particularly of the flexors. Early in the second minute the convulsions cease, often suddenly; simultaneously with their cessation, the expiratory efforts become indistinguishable, . . . and the animal lies in a state of tranquillity, which contrasts in the most striking way with the storm which preceded it. • • • • • . In these spasms which accompany the final gasps of an asphyxiated animal, the head is thrown back, the trunk straightened or arched backwards, and the limbs are extended, while the mouth gapes and the nostrils dilate. Page 321. The respiratory movements, at first natural, are gradually exaggerated, both as regards their extent and frequency. . . . . . Towards the end of the period, as in the former case, the expiratory movements gain in vigour, both absolutely and relatively to those of inspiration, so that each inspiratory act is immediately followed by a sudden tightening of the anterior abdominal wall, accompanied by convulsive twitchings of the limbs. . . . . . Suddenly the violent expulsive efforts cease and the inspiratory move- ments assume the character already described, consisting in spasmodic contractions of the diaphragm, accompanied.by gasping movements of the head and neck. Page 322.—During the convulsive struggle, and par- ticularly towards its close, the heart enlarges to something like the double of its former dimensions,—this enlarge- ment being due to the lengthening of the diastolic interval, and to the quantity of blood contained in the great veins, which in fact are so distended that if cut into they spirt like arteries. .... The effect of these changes on the arterial pressure can be best studied in a curarized animal. Page 363.—Poison a frog completely with curare Dissect out carefully one of -the large' nauscles of the thigh . . Cut away with it the piece of the pelvis to which its origin is attached. Page 395.—Introduce between the skin of the back of a strong frog a drop or two of a solution of curare. In a short time the frog will be found perfectly motionless, with its respiration arrested, but its heart still beating. Lay bare the sciatic nerve in the thigh, slip under it a pair of electrodes connected with an induction coil and stimulate the nerve with an interrupted current. If the animal has been thoroughly poisoned, no contractions whatever in the muscles of the leg will follow upon the application of a stimulus. ... If con- tractions do make their appearance, the poisoning is not complete; and the student must wait or inject a further quantity of the poison. . . . Lay bare any of the muscles of the leg and apply the electrodes directly to them. Contractions will be manifest upon the application of a very slight stimulus. In a strong frog make aii incision through the skin between the ilium and coccy.x along the line k.m. fig. 266. Cut cautiously through the ileo-coccygeal muscle until the peritoneal cavity is reached. 'Phe three nerves which go to form the sciatic nerve will come into view when the sides of the wound are held apart. Very cautiously, by means of a small aneurism needle, pass a thread under these nerves, putting it under from the outside and bringing it.out again on the median side. . . . Repeat the same process on the other side, passing the same thread under the nerve.s of that side too, but putting it in at the median side and bringing it out at the side. fide the thread very tightly round the abdomen so as to check entirely the flow of blood to the lower limbs.. All this may be done under a slight dose of chloroform . Pinching or otherwise stimulating either hind foot may produce movements in either one or both hind limbs, but in no other part of the body. Pinching or otherwise stimulating the skin of the head fore limbs or trunk above the ligature may produce move- ments in the hind limbs, but in no other part of the body. These faets are intelligible only on the hypothesis that the curare has destroyed (or suspended) the irritability of the motor nerves in that part of the body to which, by means of the blood current, it has had access, but has not destroyed the irritability of the sensory nerves or of the central nervous system. Pinching the skin of the fore limb gave rise to an afferent nervous impulse, which, either by volition or by reflex action, gave rise in turn to efferent impulses.