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§ 28. A philosophical investigation of poisons demands a complete methodical examination into their action on every life form, from the lowest to the highest. Our knowledge is more definite with regard to the action of poisons on man, dogs, cats, rabbits, and frogs than on any other species. It may be convenient here to make a few general remarks as to the action of poisons on infusoria, the cephalopoda, and insects.

Infusoria.—The infusoria are extremely sensitive to the poisonous alkaloids and other chemical agents. Strong doses of the alkaloids cause a contraction of the cell contents, and somewhat rapid disintegration of the whole body; moderate doses at first quicken the movements, then the body gets perceptibly larger, and finally, as in the first case, there is disintegration of the animal substance.

Rossbach[41] gives the following intimations of the proportion of the toxic principle necessary to cause death:—Strychnine 1 part dissolved in 1500 of water; veratrine 1 in 8000; quinine 1 in 5000; atropine 1 in 1000; the mineral acids 1 in 400–600; salts 1 in 200–300.

[41] N. J. Rossbach, Pharm. Zeitschr. für Russland, xix. 628.

The extraordinary sensitiveness of the infusoria, and the small amount of material used in such experiments, would be practically useful if there were any decided difference in the symptoms produced by different poisons. But no one could be at all certain of even the class to which the poison belongs were he to watch, without a previous knowledge of what had been added to the water, the motions of poisoned infusoria. Hence the fact is more curious than useful.

Cephalopoda.—The action of a few poisons on the cephalopoda has been investigated by M. E. Yung.[42] Curara placed on the skin had no effect, but on the branchiæ led to general paralysis. If given in even fifteen times a greater dose than necessary to kill a rabbit, it was not always fatal. Strychnine, dissolved in sea-water, in the proportion of 1 to 30,000, causes most marked symptoms. The first sign is relaxation of the chromataphore muscle and the closing of the chromataphores; the animal pales, the respiratory movements become more powerful, and at the end of a notable augmentation in their number, they fall rapidly from the normal number of 25 to 5 a minute. Then tetanus commences after a time, varying with the dose of the poison; the arm stiffens and extends in fan-like form, the entire body is convulsed, the respiration is in jerks, the animal empties his pouch, and at the end of a few minutes is dead, in a state of great muscular rigidity. If at this moment it is opened, the venous heart is found still beating. Nicotine and other poisons were experimented with, and the cephalopoda were found to be generally sensitive to the active alkaloids, and to exhibit more or less marked symptoms.

[42] Compt. Rend., t. xci. p. 306.

Insects.—The author devoted considerable time, in the autumn of 1882, to observations on the effect of certain alkaloids on the common blow-fly, thinking it possible that the insect would exhibit a sufficient series of symptoms of physiological phenomena to enable it to be used by the toxicologist as a living reagent. If so, the cheapness and ubiquity of the tiny life during a considerable portion of the year would recommend it for the purpose. Provided two blow-flies are caught and placed beneath glass shades—the one poisoned, the other not—it is surprising what a variety of symptoms can, with a little practice, be distinguished. Nevertheless, the absence of pupils, and the want of respiratory and cardiac movements, are, in an experimental point of view, defects for which no amount or variety of merely muscular symptoms can compensate.

From the nature of the case, we can only distinguish in the poisoned fly dulness or vivacity of movement, loss of power in walking on smooth surfaces, irritation of the integument, disorderly movements of the limbs, protrusion of the fleshy proboscis, and paralysis, whether of legs or wings. My experiments were chiefly made by smearing the extracts or neutral solutions of poisons on the head of the fly. In this way some of it is invariably taken into the system, partly by direct absorption, and partly by the insect’s efforts to free itself from the foreign substance, in which it uses its legs and proboscis. For the symptoms witnessed after the application of saponin, digitalin, and aconitine, the reader is referred to the articles on those substances.

In poisoning by sausages, bad meat, curarine, and in obscure cases generally, in the present state of science, experiments on living animals are absolutely necessary. In this, and in this way only, in very many instances, can the expert prove the presence of zymotic, or show the absence of chemical poison.

The Vivisection Act, however, effectually precludes the use of life-tests in England save in licensed institutions. Hence the “methods” of applying life-tests described in former editions will be omitted.

§ 29. Effect of poisons on the heart of Cold-blooded Animals.—The Vivisection Act does not, however, interfere with the use of certain living tests, such, for instance, as the testing of the action of poisons upon the recently extirpated hearts of cold-blooded animals.

Williams’ Apparatus.

The heart of the frog, of the turtle, of the tortoise, and of the shark will beat regularly for a long time after removal from the body, if supplied with a regular stream of nutrient fluid. The fluids used for this purpose are the blood of the herbivora diluted with common salt solution, or a serum albumin solution, or a 2 per cent. solution of gum arabic in which red blood corpuscles are suspended. The simplest apparatus to use is that known as “Williams’.” Williams’ apparatus consists of two glass bulbs (see diagram), the one, P, containing nutrient fluid to which a known quantity of the poison has been added; the other, N, containing the same fluid but to which no poison has been added; these bulbs are connected by caoutchouc tubing to a three-way tube, T, and each piece of caoutchouc tubing has a pressure screw clip, V¹ and V; the three-way tube is connected with a wider tube containing a valve float, F, which gives free passage of fluid in one direction only, that is, in the direction of the arrow; this last wide tube is connected with a Y piece of tubing, which again is connected with the aorta of the heart under examination, the other leg of the Y tube is connected with another wide tube, X, having a float valve, F²: the float containing a drop of mercury and permitting (like the float valve F) passage in one direction only of fluid, it is obvious that if the clip communicating with N is opened and the clip communicating with P is closed, the normal fluid will circulate alone through the heart; if, on the other hand, the P clip is open and the N clip closed, the poisoned blood will alone feed the heart. It is also clear that by raising or depressing the bulbs, the circulating fluid can be delivered at any pressure, high or low. Should a bubble of air get into the tubes, it can be got rid of by removing the cork at S and bringing the fluid up to the level of the top of the aperture. The observation is made by first ascertaining the number and character of the beats when the normal fluid is circulating, and then afterwards when the normal is replaced by the poisoned fluid. A simpler but less accurate process is to pith two frogs, excise their respective hearts, and place the hearts in watch-glasses containing either serum or a solution of common salt (strength 0·75 per cent.); to the one heart is now added a solution of the poison under examination, and the difference in the behaviour and character of the beats noted.

The phenomena to be specially looked for are the following:—

1 The heart at the height of the poisoning is arrested in diastole.

2 The heart at the height of the poisoning is arrested in systole.

Arrest in diastole.—The arrest may be preceded by the contractions becoming weaker and weaker, or after the so-called heart peristalsis; or it may be preceded by a condition in which the auricle shows a different frequency to the ventricle.

The final diastole may be the diastole of paralysis or the diastole of irritation.

The diastole of irritation is produced by a stimulus of the inhibitory ganglia, and only occurs after poisoning by the muscarine group of poisons. This condition may be recognised by the fact that contraction may be excited by mechanical and electrical stimuli or by the application of atropine solution; the latter paralyses the inhibitory nervous centres, and therefore sets the mechanism going again. The diastole of paralysis is the most frequent form of death. It may readily be distinguished from the muscarine diastole; for, in muscarine diastole, the heart is full of blood and larger than normal; but in the paralytic form the heart is not fully extended, besides which, although, if normal blood replace that which is poisoned, the beats may be restored for a short time, the response is incomplete, and the end is the same; besides which, atropine does not restore the beats. The diastole of paralysis may depend on paralysis of the so-called excito-motor ganglia (as with iodal), or from paralysis of the muscular structure (as with copper).

§ 30. The effect of poisons on the iris.—Several poisons affect the pupil, causing either contraction or dilatation. The most suitable animal is the cat; the pupil of the cat readily showing either state.

Toxic myosis, or toxic contraction of the pupil.—There are two forms of toxic myosis, one of which is central in its origin. In this form, should the poison be applied to the eye itself, no marked contraction follows; the poison must be swallowed or injected subcutaneously to produce an effect. The contraction remains until death.

The contraction in such a case is considered to be due to a paralysis of the dilatation centre; it is a “myosis paralytica centralis;” the best example of this is the contraction of the pupil caused by morphine.

In the second case the poison, whether applied direct to the eye or entering the circulation by subcutaneous injection, contracts the pupil; the contraction persists if the eye is extirpated, but in all cases the contraction may be changed into dilatation by the use of atropine. An example of this kind of myosis is the action of muscarine. It is dependent on the stimulation of the ends of the nerves which contract the pupil, especially the ends of the nervus oculomotorius supplying the sphincter iridis; this form of myosis is called myosis spastica periphera. A variety of this form is the myosis spastica muscularis, depending on stimulation of the musc. sphincter iridis, seen in poisoning by physostigmine. This causes strong contraction of the pupil when locally applied; the contraction is not influenced by small local applications of atropine, but it may be changed to dilatation by high doses. Subcutaneous injection of small doses of physostigmine does not alter the pupil, but large poisonous doses contracts the pupil in a marked manner.

Toxic mydriasis, or toxic dilatation of the pupil.—The following varieties are to be noticed:—

1. Toxic doses taken by the mouth or given by subcutaneous injection give rise to strong dilatation; this vanishes before death, giving place to moderate contraction. This form is due to stimulation of the dilatation centre, later passing into paralysis. An example is found in the action of aconite.

2. After subcutaneous or local application, a dilatation neutralised by physostigmine in moderate doses. This is characteristic of β-tetrahydronaphthylamine.

3. After subcutaneous injection, or if applied locally in very small doses, dilatation occurs persisting to death. Large doses of physostigmine neutralise the dilatation, but it is not influenced by muscarine or pilocarpine: this form is characteristic of atropine, and it has been called mydriasis paralytica periphera.

The heart at the height of the poisoning stops in systole.

2. Arrest in systole.—The systole preceding the arrest is far stronger than normal, the ventricle often contracting up into a little lump. Contraction of this kind is specially to be seen in poisoning by digitalis. In poisoning by digitalis the ventricle is arrested before the auricle; in muscarine poisoning the auricle stops before the ventricle. If the reservoir of Williams’ apparatus is raised so as to increase the pressure within the ventricle the beat may be restored for a time, to again cease.

A frog’s heart under the influence of any poison may be finally divided into pieces so as to ascertain if any parts still contract; the significance of this is, that the particular ganglion supplying that portion of the heart has not been affected: the chief ganglia to be looked for are Remak’s, on the boundary of the sinus and auricle; Ludwig’s, on the auricle and the septum of the auricle; Bidder’s, on the atrioventricular border, especially in the valves; and Dogiel’s ganglion, between the muscular fibres. According to Dogiel, poisons acting like muscarine affect every portion of the heart, and atropine restores the contractile power of every portion.