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the liver were made immediately after death, and the proportion of glycogenic matter, not sugar, was estimated. His results are, consequently, much more reliable and satisfactory. In a number of analyses of the livers of dogs confined to different articles of diet, Pavy found a little over seven per cent. of glycogenic matter, upon a diet of animal food; over seventeen per cent., upon a diet of vegetable food; and fourteen and a half per cent., upon a diet of animal food and sugar.' These results have been confirmed by M'Donnell, who, in addition, found that hardly a trace of amyloid substance could be detected in the liver on a diet of fat, and none whatever upon a diet of gelatine.' Bernard had already observed that the amount of sugar produced by the liver on a diet of fat was the same as during total abstinence from food. These facts are entirely in accordance with observations upon the effects of different kinds of food in diabetes, and they have an important bearing upon the dietetic measures to be employed in this disease.

The effect of entire deprivation of food is to arrest the production of sugar in the liver, three or four days before death. This arrest of the glycogenic function has generally been observed in cases of disease, except when death has occurred suddenly.

Influence of the Nervous System, etc.- Bernard has studied the influence of the nervous system upon the production of sugar more satisfactorily than any other of the variations of the glycogenic function, for the reason that he has noted these modifications by determining the sugar in the blood and the urine. Some of the points with regard to the nervous system we will consider again in another volume; and it is sufficient, in this connection, to mention the

1 PAVY, op. cit., p. 33, et seq.

M'DONNELL, Observations on the Functions of the Liver, Dublin, 1865, p. 14. 3 BERNARD, Leçons de physiologie expérimentale, Paris, 1855, p. 137. 4 BERNARD, op. cit., p. 129.

main results of some of the most striking of the experiments on this subject.

FIG. 13.

The most remarkable experiment upon the influence of the nervous system on the liver is the one in which artificial diabetes is produced by irritation of the floor of the fourth ventricle. This operation is not difficult, and is one that we have often repeated. The instrument used is a delicate stilet, with a flat cutting extremity, and a small projecting point, about of an inch long.' In performing the operation upon a rabbit, the head of the animal is firmly held in the left hand, and the skull is penetrated in the median line, just behind the superior occipital protuberance. This can easily be done by a few lateral movements of the instrument. Once within the cranium, the instrument is passed obliquely downward and forward, so as to cross an imaginary line between the two auditory canals, until its point reaches the basilar process of the occipital bone. The point then penetrates the medulla oblongata, between the roots of the auditory nerves and the pneumogastrics, and, by its projection, serves to protect the nervous centre from more serious injury from the cutting edge. The instrument is then carefully withdrawn, and the operation is completed.' This ex-turing the floor of periment is almost painless, and it is not desirable to administer an anæsthetic, as this, in itself, would disturb the glycogenic process. The urine may be drawn before the operation, by pressing the lower part of the abdomen, taking care not to

Instrument for punc

the fourth ventricle

(BERNARD. Leçons périmentale, Paris,

de physiologie

1855, p. 290).

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1 These instruments have been made by Messrs. Tiemann & Co., of this city. BERNARD, Leçons de physiologie expérimentale, Paris, 1855, p. 291, et seq.

allow the bladder to pass up above the point of pressure, and it will be found turbid, alkaline, and without sugar. In one or two hours after the operation, the urine will have become clear, acid, and will react readily with any of the copper-tests. When this operation is performed without injuring the adjacent organs, the presence of sugar in the urine is only temporary, and the next day, the secretion

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Section of the head of a rabbit, showing the operation of puncturing the floor of the fourth ventricle. a, cerebellum; b, origin of the seventh pair of nerves; c, spinal cord; d. origin of the pneumogastric; e, opening of entrance of the instrument into the cranium: f. instrument; 9. fifth pair of nerves; h, auditory canal; i, extremity of the instrument on the spinal cord after having penetrated the cerebellum; k. occipital venous sinus; . tubercula quadrigemina; m, cerebrum; n, section of the atlas. -(BERNARD, Leçons de physiologie expérimentale, Paris, 1855, p. 293.)

will have returned to its normal condition. It is best, in performing this experiment, to operate on an animal in full digestion, when the production of sugar is at its maximum.

The production of diabetes in this way, in animals, is exceedingly interesting in its relations to certain cases of the disease in the human subject, in which the affection is traumatic, and directly attributable to injury near the medulla.

Its mechanism it is difficult to explain. The irritation is not propagated through the pneumogastric nerves, for the experiment succeeds after both of these nerves have been divided; but the influence of the pneumogastrics upon glycogenesis is curious and interesting. If both of these nerves be divided in the neck, in a few hours or days, depending upon the length of time that the animal survives the operation, no sugar is to be found in the liver, and there is reason to believe that the glycogenic function is arrested. After division of the nerves in this situation, galvanization of their peripheral ends does not affect the production of sugar; but, by galvanization of the central ends, an impression is conveyed to the nervous centre, which is reflected to the liver, and produces a hypersecretion of sugar.' These questions will be referred to again, in connection with the physiology of the nervous system.

With regard to the influence of the sympathetic system upon the glycogenic function, there have been few experiments which lead to conclusions of any great value. Pavy found that division of the sympathetic filaments accompanying the vertebral arteries produced diabetes, but the operation was complicated by lesions of the vessels, which rendered the results somewhat unsatisfactory.'

It has been observed that the inhalation of anæsthetics and irritating vapors produces temporary diabetes; and this has been attributed to the irritation conveyed by the pneumogastrics to the nerve-centre, and reflected, in the form of a stimulus, to the liver. It is for this reason that we should avoid the administration of anaesthetics in all accurate experiments on the glycogenic function. In illustration of this fact, Pavy has collected twenty cases, in which

1 BERNARD, loc. cit., p. 317.

BERNARD, op. cit., p. 324. It has been observed by Bernard that division of the pneumogastrics in the chest, between the lungs and the liver, does not affect the production of sugar (p. 328).

3 PAVY, op. cit., p. 87, et seq.

4 BERNARD, op. cit., p. 327.

chloroform was administered in the human subject for surgi cal operations, in all of which the passage of a small quantity of sugar in the urine was noted.'

Destination of Sugar.-Although sugar is constantly produced by the liver and taken up by the circulation, it is exceptional to find it in the blood after it has passed through the lungs. It is difficult to ascertain the precise mode of its destruction in the lungs, and, indeed, the nutritive function of sugar in the economy is not thoroughly understood. All that we can say of the destination of liver-sugar is, that it probably has the same office in nutrition as the sugar taken as food and that resulting from the digestion of amylaceous matters. The facts bearing upon this question will be reviewed under the head of nutrition.

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Alleged Production of Fat by the Liver.-It is stated by Bernard, that in animals fed largely with saccharine and amylaceous principles, the blood of the hepatic veins contains an emulsive matter, which seems to be fat combined with a proteine substance. In support of the opinion that fat is thus produced in the liver, he brings forward that wellknown fact, that a diet of starch and sugar is particularly favorable to the development of adipose tissue.' But the examinations of the matter supposed to be fatty have not been sufficiently minute to lead to any positive conclusions with regard to its character or composition. Rouget states, unreservedly, that this substance is simply glycogenic or amyloid matter." While there can be no doubt of the formation of fat in the organism independently of the fat taken as food, there is not sufficient ground for regarding the liver as one of the organs specially concerned in its production.

1 Op. cit., p. 80.

BERNARD, Leçons de physiologie expérimentale, Paris, 1855, p. 154.

3 ROUGET, Des substances amyloides.-Journal de la physiologie, Paris, 1859, tome ii., p. 324.

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