physiological point of view this epithelium is remarkable for

its impermeability; it absolutely opposes the transmission of liquids. A solution of belladonna may be kept in a perfectly healthy bladder for a long time, without risk of poisoning from atropine; so, also, may solutions of opium, without danger of opium poisoning. But if the epithelium is diseased, absorption immediately occurs;

d

and, as an example, when Fig. 128. —Epithelium of the bladder.* dilute alcohol is injected into the bladder in which there exists catarrhal inflammation, symptoms of alcoholic intoxication are manifested. The vesical epithelium even for some hours after death preserves its vitality and consequently its impermeability. If ferro-cyanide of potassium be injected through a tube, thus preventing contact with the urethral mucous surface, into the bladder of an animal which has just been killed, then the bladder be exposed and a ferric salt placed upon the outside of its walls, no Prussian blue will be seen. This experiment shows that the two salts, which in contact would produce Prussian blue, are separated by an impassable barrier, viz., the epithelium. Yet if by means of a wire the epithelial coat on the inside of the bladder be scratched or destroyed at this point, Prussian blue will be immediately formed. This opposition, then, to the passage of liquids results solely from the presence of the epithelium.1 The muscular fibres of the bladder are smooth, and

66

1 For a further verification and elucidation of the above statement the reader is referred to Ch. Robin, "Leçons sur les Humeurs." 1867, p. 22. Also, see J. J. C. Susini, De l'Imperméabilité de l'Epithelium Vésical." Thèse de Strasbourg, 1857, No. 30. The epithelium of the urethra being much less resisting, and possessing a different character (columnar and pavement cells), permits absorption. (See Alling, Thèse de Paris, 1871.)

a, Voluminous cell, with the edges notched; smaller spindle-shaped cells are attached to these edges. b, Analogous cells; the most voluminous has two nuclei. c, A still larger cell, irregularly quadrilateral, with four nuclei. d, Analogous cell, as seen in front, with two nuclei, and pitted, the pits corresponding to the notches of the edges, above. (Virchow, "Path. Cell.," and "Archiv. für Pathol. Anat." Vol. III. Tab. 1, Fig. 8.)

consequently have slow and lazy contractions; but they are, moreover, very elastic, and allow the bladder to dilate readily, as well as the urine to accumulate in large quantity. When this dilatation is pushed to its extreme extent, it becomes a cause of irritation to the muscular fibre, which will then contract, and the bladder expel its contents. We shall soon see that this reaction occasions a desire to urinate. When there is inflammation of the bladder, its muscular walls are less elastic (see Physiology of the Muscle), and these more quickly react upon the contents of the reservoir, and occasion in such cases frequent desire for micturition.

The important question now presents itself as to how the urine, during the quiescence of the bladder, is retained in this reservoir and does not escape through the orifice in the neck of the bladder. We all know that this is closed by a contraction of the vesical sphincter which surrounds the opening; but these muscular fibres are not very pronounced, nor can a muscle be kept in a continual state of contraction. The neck of the bladder is closed, because this is its natural form, like that of other and similar circular muscles; these obliterate the orifice which they circumscribe, when they are in a state of repose, and this is simply due to their elasticity. But so soon as some cause opposes this sphincter, it becomes powerless to prevent the passage, which the urine overcomes and rushes through. With women this orifice is differently arranged, and on a slight effort, Vs or burst of laughter, several drops of urine may gush out. Certain Up arrangements and especial positions of the bladder, especially in man, are of such a nature that there exists no real orifice while the bladder is in a state of repose.

S ps

B

Fig. 129.

V

Cd

Bladder and organs of micturition.*

First, the axis of the bladder (Fig. 129) is by no means vertical, but almost horizontal (this organ rests upon the symphysis pubis, which has almost a horizontal position); the excretory

*S, Symphisis pubis. ps, Plexus of Santorini. V, Bladder. O, Remains of the urachus. Pp, Prostrate gland. Up, Prostatic utricle. Cd, Deferent canal. Vs, Vesiculæ seminales, whose neck joins with the deferent canal to form the excretory duct, which may be seen going behind the prostatic utricle. W, The so-called Wilson's muscle (pubo-urethral band). Gp, Cowper's gland. B, Bulb of the urethra.

canal, urethra, has first a position vertically downwards, then it turns and curves forwards; thus, this canal is liable to be compressed by the enormous distention of the bladder.

Again, the prostate gland (Pp, Fig. 129) is a hard unyielding organ, being composed of glands, fibrous tissue, and muscular elements; this urethral opening penetrates and is encircled by this prostate gland in such way as to have its walls closed by contact. This forms the principal cause in man of the retention of urine during the inaction of the bladder. Should the prostate gland become hypertrophied, a still greater obstacle (too much so in old men) is made to the passage of urine, and becomes the cause of a pathological retention.

Finally, the flattening of the urethral canal and its closure by contact are influenced by the arrangement of the perineal fascia, the fibres of which press upon the sides of the urethral canal in their course from the ischium to the pubis; and a certain muscular and expulsive effort is required to overcome this constraint, and dilate the orifice.

It is not surprising in view of this explanation that the urine is allowed to accumulate in this muscular, dilatable, and elastic reservoir, and that no physiological act or contraction is required to prevent the exit of the urine; these conditions are simply mechanical and continue after death, since urine is often found in the bladder of the dead body.

ena.

When the walls of the bladder become too much distended by the presence of urine, we have said that a compression of the contents is produced by contraction of the smooth muscular fibres; this overcomes the elasticity of the neck of the bladder and of the prostate, and the urine passes into the bulbous portion of the urethra: here it comes in contact with a very sensitive mucous surface, the prostatic mucous membrane, which presides over a large number of reflex phenomIt is owing to this contact of the urine with the mucous surface that we experience that peculiar sensation of a necessity or desire for micturition, and which we refer, in common with almost all other sensations of this region, to the fossa navicularis. If we pay no attention to this desire, a reflex irritation is produced, which is followed by the contraction of the constrictor urethræ, or urethral sphincter; the urine can then go no farther, and is even obliged to retrograde, on account of the contraction of the muscles on the anterior portion of the prostate, and so re-enters the bladder whose contractions have ceased.

These co-ordinated contractions, which occasion micturition, are made under the influence of the spinal cord, and particularly its lumbar portion. Budge has sought to fix the precise seat of this centre, and by experiments has placed the centre of innervation of the bladder in the fourth lumbar vertebra (in dogs and rabbits). Kupresson localizes this centre between the fifth and sixth lumbar vertebræ.

Sensibility of the prostatic mucous surface is very important, since this is the point of origin for the essential reflex action; loss of this sensibility is the cause of that form of incontinence of urine called enuresis, or nocturnal incontinence; this involuntary voiding of urine, as in similar cases of involuntary emission of feces, is explained by the lack of sensibility of the mucous surfaces to the contact of excrementitial products, and in this particular case, the absence of a premonitory sensation of the desire to urinate.

Some moments after the continued distention of the vesical reservoir, it reacts anew, and the urine proceeds to the prostatic portion of the urethra, where it stimulates anew the same reflex action, and so on. This explains the intermittent form of the desire for micturition. If these phenomena are often repeated, the reflex contraction of the urethral sphincter gradually loses its energy, and the urine tends to pass out through the urethral canal; hence the distress occasioned by resisting the desire to urinate. Thus it is seen that every time a true active resistance is offered to the passage of urine, this opposition is made, not by the sphincter of the bladder, but by the sphincter of the urethra, the constrictor urethra muscle, which is the only one of these muscles which is striated or voluntary.1

If a sound be introduced into the urethra, as soon as its tip touches the mucous membrane of the prostatic portion, it will occasion a sensation similar to the desire to urinate; we refer this sensation to the other extremity of the urethra, simply because it is one of those associated sensations, examples of which we have already cited. (See General Sensibility and Sensations, pp. 79 and 388.)

When we yield to the desire, in spite of the absence of any obstacle on the part of the sphincter or constrictor urethræ, we cannot completely evacuate the contents of the bladder by the simple contraction of its walls. We must

1 See Carayon, "De la Miction dans ses Rapports avec la Physiologie et la Pathologie." Thèse de Strasbourg, 1865, No. 814.

1

2

V 3

call in to our assistance the abdominal muscles, by means of which the abdominal viscera will press upon the bladder and increase the expulsive efforts of its walls. We close the glottis at the very beginning of micturition, and then the vesical contraction is sufficient for the expulsion of urine. But towards the end of micturition, in order to expel the last drops, a renewed effort is necessary: the lowest portion of the bladder being fixed and concave, we could not evacuate it completely, unless, by the aid of the abdominal muscle, we compress the upper against the lower portion of the bladder in such a way as to completely obliterate the cavity (Fig. 130); in man, then, the bladder when completely

W

emptied (not so, however, with all ani- Fig. 101.- Diagram of mals) resembles a cup, and in this form

micturition.*

it is seen in the dead body when this reservoir is completely empty.

As soon as the bladder has been emptied, the walls of the urethra are brought in contact and expel its contents; but when this canal is diseased and long-seated inflammation has destroyed the elasticity of the bladder, it is not thoroughly emptied, and the urine remaining in contact with the mucous surface, contributes to keep up the pathological condition.

II. GENITAL SYSTEM.

I. MALE ORGANS OF GENERATION.

THE male organs of generation are composed of a gland (testicle) and a series of excretory ducts.

1. The male gland, the testicle, is the offshoot from an organ which is developed on the inner edge of the Wolffian body (see above); until the close of the second month this body presents no characteristic feature that would lead us to know whether it were a testicle or au ovary; but towards

*This diagram shows how the bladder is completely emptied.

1, Outline of the bladder when distended by a liquid. 2, 3, 4, 5, Represents the outline of the bladder when reduced by different intensities of its contractions. 6, Represents the outline when the abdominal muscles have adjusted the upper to the lower concave portion. The arrow indicates the direction in which the compression is made.