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38. Such unwonted efforts of the orbital muscles entail collateral effects. As we strain the eye with a divergent or convergent pencil in use, we see that the iris at the moment that the orbital muscles most violently pull upon the ball, contracts greatly. It may be because the retina is practically, as to objective light, darkened, but more probably from consentaneous muscular action. I have nobody at hand conversant with the laws of optics to watch the conduct of the images of a flame from reflections at the cornea, and two surfaces of the crystalline lens for me when I strain my eye. But I have no doubt that one or more of them would exhibit some instructive variations in aspect. An intelligent observer, whom I had not previously told what sort of changes to look for, was struck with the dilatation of the pupil, and so particularly with the behaviour of the posterior inverted image, that he always forgot to notice the others. At the instant of spasmodic strain, as the pupil enlarged, the inverted image, as he expressed it, “dilated and retreated from his view, even quite from his view;" as if the lens became flattened behind.

39. Under the torture the ocular tunics become painful; the orbicular and levator palpebræ muscles, as well as those attached to the ball within and without it, become excessively fatigued and sore; so that the eyes seem to weigh down, and any use of them oppressive. This soreness may burthen us for hours and even days. Since the time of Mesmer the train of phenomena here detailed has been widely experienced. And the flitting away of objects from the field of view has been described by physiologists as irradiation” or “extension of sensation,” as if the lucid impression made upon a large area of sentients might also affect a limited number included by them, not touched by the light. This would be a visual defect, of which it is now plain we have no reason to accuse the retina.*

40. There is a certain period as the evening is closing in when, as we wink the eye, every separation of the lids is attended with a phantom of the central hole of the retina, that looks like a shadow of it. Now when the light has waned a little fainter still, we fail to see white objects not extending more than 4° at the eye (33) with direct vision, when we see them plainly with oblique, intimating that the region of the hole is less sensible to weak lucid impressions than other parts. From which it may be deduced that the foregoing shadowy

. appearance arises from the circumstance that the retina at the hole, in light of just force enough to enable it to see as well as at other parts, requires a moment longer to be equally affected by it. This is a longknown phenomenon, and I believe has generally been properly understood. It is not a shadow of the brim of the hole exclusively (33), for it comes forth just when light is too scanty to enable us to catch the shadow of the vessels by wiuking; yet it looks sometimes annular, as if the shadow were associated with it.

Ocular Spectres, &c., p. 56. I cannot find the slightest trace that the true nature of this series of phenomena had ever been suspected by other observers ; unless a suggestion of Donders, that pressure upon the eye lessens the sensibility of the retina, by checking its supply of blood, be a correct indication.

| Brewster's Optics, p. 418. 47-XXIV.

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41. I have now discussed, as far as I am aware of, all the essential mechanical disturbances of retinal action, and optical indices of a differential constitution in the bed of sentients. With a few words on the probable properties and seat of the sentients I shall bring this paper to an end.

Our visual experience teaches us that the region of the foramen centrale possesses usually the highest distinguishing power, and that this power gradually diminishes from it through the punctum aureum to the ora serrata. This ratio of diminution is perhaps proportional to that of the number of cones (not rods) that may be counted in equal areas from centre to circumference. Which suggests, that with an allowance for the peculiar central spot, the cones may be the true sentients, whilst the rods may assist or not. They are also normals to the retina, as seems necessary in the ultimate sentients. The law of isolation of sensation is absolutely stringent all over the retina, which seems to require the nerve to end in a mosaic bed of nervous bodies. In the anatomy of the retina, the radial fibres appear to be of non-nervous substance, and they issue from the internal centres of the rods and cones to connect them with the limitary membrane. If one or both of these latter, therefore, is the sentient, it is not unlikely that there is an obstacle to its action at the tip. We might conjecture from this, that the elements of conical. form are the sentients, and that they act at their sides an idea confirmed by the most sensible part being lodged in a pit, and presenting a direct unveiled surface to light. The sentients are behind the vasa centralia, at a calculated distance that agrees with the actual interval fonnd between them and the vessels. Light falling posteriorly to a certain point would not affect the sentients, for pressure through the tunics evinces that it is only anteriorly that they respond to stimulus. This pressure also (34) showing that quasi-luminous appearances are produced by creasing the inner part of the retina, accords very nicely with the hypothesis that the sentients are cones pointing inwards, and that generally the sentient surfaces are in little cavities walled round, after the type of the foramen centrale. Such are the arguments that occur to me for assigning the office of receiving sensations from light to the cones.*

ART. II.
On the Simultaneous Existence in the Human System of Two or more

Diseases, which are supposed to originate from Specific Morbid
Poisons. By CHARLES MURCHISON, M.D., L.R.C.P., Assistant-
Physician to King's College Hospital and the London Fever

Hospital. PERHAPS in no science more than in that of medicine, do preconceived opinions lead to an erroneous interpretation of facts, and in none is it more necessary that doctrines which are generally accepted should have a firm and sure foundation. Take an illustration from the subject before us. There is a prevalent belief in the profession that no two of those febrile diseases, which are thought to depend upon the introduction of a morbid poison into the blood, can exist in the system at one and the same time; and this doctrine has been turned to account as an argument against the non-identity of typhus and pythogenic* fever. Cases have been described in which the eruptions of these two fevers have co-existed, and have been adduced as positive proofs that the poisons of the two fevers must be identical. But if the doctrine upon which the argument is founded be erroneous, the force of the latter immediately disappears.

* In the first part of this paper three fractions were incompletely printed from slipping of the tyre. At p. 474, line 17, the fraction should be stu; at 476, line 29, the fraction d'o; and at line 30, the fraction at

The doctrine itself originated from high authority, being first propounded by John Hunter. Before him, Adams tells us "it was overlooked.” Hunter adduced several instances, in which he thought the introduction of a second poison arrested the progress of a previous one, and he drew the conclusion that “no two of them can exist in the same part of the body at the same time;" and that in the case of the eruptive diseases which“ are necessarily the consequence of fever, it is impossible at the same time for the two to have their respective eruptions, even in different parts, because it is impossible that the two preceding fevers should be co-existent.”+ The law laid down by Hunter was subsequently confirmed by Joseph Adams, who in his admirable Observations on Morbid Poisons, although he alludes to certain instances in which two such poisons did co-exist, yet considered these as only exceptions which proved the law. So early as 1801, however, the opinion of Hunter was strenuously opposed by John Ring, who collected, in his work on Vaccination, f numerous cases to show “that two morbid actions and two eruptive diseases can co-exist.” A similar opinion has in more recent times been held by Dr. Robert Williams, who has brought forward many examples of the co-existence in the same individual of two of the eruptive fevers. Many isolated instances also, illustrative of the same point, have been recorded in the medical journals and periodicals, both English and foreign. Still the prevalent opinion in the profession is, as above stated, opposed to the doctrine of the possibility of co-existence. It is purposed, therefore, here to collect a portion of the evidence bearing upon the question, this evidence being derived partly from the experience of others, and partly from my own observation.

A. Variola and Scarlatina.—The co-existence of these two diseases has been alluded to by several systematic writers. The author of the article · Variole,' in the 'Dictionnaire de Médecine,'|| observes :—“La variole peut être compliquée accidentellement avec la rougeole, la scarlatine, et plus souvent avec le purpura bæmorrhagica." Dr. Gregory observed at the Small-Pox Hospital “ several unequivocal

The term pythogenic is synonymous with typhoid, and has been proposed as a substitute for the latter, for reasons which will be found in a paper on the Classification of Fevers, in the Edinburgh Medical Journal, Oct. 1858.

† Hunter's Works, edited by Palmer, vol. i. p. 313; and vol. iii. p. 4. Treatise on the Cow-pox, 1801-3, p. 1029. $ On Morbid Poisons.

# Deuxième édition, 1846, tome xxx. p. 573.

1836.

cases of the simultaneous existence of small-pox and scarlatina anginosa. Williams maintained that the variolous poison was capable of co-existing with many other poisons, and among others, with scarlatina; and Erasmus Wilson remarks: "Variola is occasionally complicated with rubeola and scarlatina." Lastly, Dr. Copland quotes several authorities to prove that "scarlet-fever has been seen co-existing with variola, both distempers pursuing their regular courses."§

Examples of the co-existence of these two diseases may be divided into-1. Those in which the scarlet-fever has first manifested itself. 2. Those in which the manifestation of the scarlet fever and variola has been simultaneous. And 3. Those in which the indications of the variolous poison have preceded those of the scarlet-fever. The following are examples of the first class:

Illustration I.—An infant under the care of M. Revolat of Bordeaux. In the course of an attack of scarlatina, and while the scarlet rash was well out, variolous pustules appeared, first in the lower extremities, and on the following day on the face, tongue, and fauces, so as to impede deglutition.||

Illustration II.-In the 'Gazette des Hôpitaux' for 1842, a case is mentioned of an infant aged three years, who had been under the care of M. Baudelocque for scarlet-fever, and in whom a varioloid eruption appeared on the twenty-fifth day from the first appearance of the scarlet rash. The child had been vaccinated.

Illustration III.-For the particulars of the following case I am indebted to Dr. Walshe. Most complete details of it are recorded in the case-books of University College Hospital.** A female, aged twenty, was admitted June 23rd, 1847. She had been vaccinated satisfactorily, and had had both measles and scarlet-fever, but never small-pox. She had not been exposed to any traceable contagion. June 19th.-Went to bed perfectly well.

June 20th.-Vomiting, violent headache, coryza, and suffusion of

eyes.

June 21st.-Pains in back and loins, and in afternoon a wellmarked scarlet rash, appearing first on the face and then on the arms and shoulders.

June 22nd.-Headache gone; still very sick; rash more distinct. June 23rd (fourth day).—Pulse 104; respiration 38; much lumbar pain; conjunctivæ injected; much coryza; tongue with a thick white fur; voice hoarse; throat sore; a sensation of choking; right tonsil red and enlarged; face bright-red; and a purplish efflorescence, slightly raised, and at some places crescentic, on shoulders, chest, and abdomen.

June 24th (fifth day).-Pulse 120; respiration 34; tongue with Cyclopædia of Practical Medicine, vol. iii. p. 744. † Op. cit., vol. i. p. 211.

Diseases of the Skin, p. 84.

§ Dictionary of Practical Medicine, vol. iii. p. 819.

Copied from Journ. de Méd. de Bourdeaux, in Gaz. Méd. de Paris, 1832, vol. v. p. 411. Deuxième série, tome iv. p. 74. ** Female Case Book, vol. ii. p. 217. 1847.

yellowish-brown fur; throat much sorer, and both tonsils ulcerated ; has passed two and a half " chamber-pots" full of blood per vaginam; skin very hot; face swollen; neck, chest, and fore-arms of a general uniform red tint; on left arm a number of papules, size of a split-pea, and in front of either wrist from ten to fifteen vesicles containing opalescent fluid.

June 25th (6th day).-Pulse 120; respiration 32; intellect clear; tongue almost clean, and voice improved; face less swollen, and has lost its bright red hue, but on forehead are innumerable purple petechiæ, varying in size from a pin's head to a mere point; efflorescence on arms less bright; vesicles much increased in number, and at some places passing into pustules, and distinctly umbilicated.

June 26th (seventh day).-Pulse 120; restless and delirious in night; much dysphagia and blood in stools; purple spots on face increased, and some ecchymotic spots on legs.

June 27th (eighth day).-Pulse 152; face very swollen and livid, with numerous petechiæ; an abrasion of left cheek, discharging bloody serosity; petechiae and ecchymoses general over body; lips dry and brown; still discharge of blood per rectum et vaginam; sensible until a quarter of an hour of death, at one P.M.

On post-mortem examination, the tonsils, pharynx, and posterior nares were found large, prominent, and disorganized into a putrid greenish detritus; the epiglottis, larynx, and trachea were covered with punctiform ecchymoses, and there were numerous blood-coloured spots at base of right lung; there were also deep ecchymoses of the mucous membrane of the stomach, of the lowest thirty inches of the ileum, and of the large intestine, as also in the pelvis of the right kidney, and beneath the lining membrane of the portal vein. The blood was fluid, and the coats of the vessels generally stained.

Illustration IV.-A female servant, aged twenty-two, was admitted into the London Fever Hospital, February 7th, 1855; had had measles and scarlet-fever—the latter ten years before. No record taken as to vaccination.

Feb. 4th.-Rigors, vertigo, and headache.

Feb. 7th.-On admission, pulse 112; respiration 28; tongue red at tip, with thick white fur; a characteristic scarlet eruption on face, arms, trunk, and about knees; face swollen.

Feb. 8th.-Pulse 96; a number of hard papules on face and a few on trunk; scarlet rash disappeared from breasts, but copious on arms and legs; much headache; no sore throat or dysphagia; tongue with thick white fur and prominent red papillæ.

Feb. 10th.-Still some scarlet rash on neck; some of papules contain lymph, others pus.

Feb. 11th. Some sore throat, and a trace of albumen in urine. Feb. 12th.-Pulse 80; sore throat and albuminuria gone; pustules on face and arms continue; desquamation of cuticle on fore-arms. Feb. 14th. Desquamation on arms continues; pustules dis

appearing.

Feb. 23rd.-Discharged well.

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