«A SUGGESTION AS TO THE CAUSE OF THE ASPER- MATIC CONDITION OF THE IMPERFECTLY DESCENDED TESTIS BY F. A. E. CREW, M.D., D.Sc. (Paper from the Animal ...»
Russell Howard records that of twenty-seven cases of malignant disease of the testis, nine had occurred in imperfectly descended glands.
It would seem that when the testis occupies its normal position in the scrotum, the conditions are such that the activities of the other component tissues of the gland are restrained by the dominating activity of the germinal epithelium, but that when the testis is brought to rest in an abnormal situation, the function of spermatogenesis being in abeyance, the other tissues of the gonad take on an uncontrolled growth.
Griffiths, in an experimental investigation on dogs, found that when the testes of the puppy were replaced within the abdominal cavity they developed normally up to the time of puberty but that they never produced spermatozoa, and that when the testes of grown dogs were similarly replaced within the abdomen they invariably atrophied and never remained functional.
In those mammals in which the testis periodically passes into a scrotum Aspermatic Condition of the Imperfectly Descended Testis 103 during the breeding period, it is found that they are spermatic only when in the scrotum, and aspermatic when within the abdomen.
To explain the relation between imperfect descent and imperfect functioning there are two theories: one, that the imperfection in functioning is the cause of the imperfect descent, the other, that it is the result. The first postulates that there is some abnormality of the germinal epithelium which prevents the normal development and migration. If this is so, then obviously no operative treatment can possibly restore the spermatogenic function. The second explanation is that full growth and development of the testis up to the time of puberty is possible in an abnormal situation, but that at the time when the final stages of spermatogenesis should occur, the abnormal situation reacts upon the testis in some way so that these stages cannot occur and atrophy of the testis ensues while various pathological processes easily attack the gland leading to degeneration and tumour growth. If the fault lies with the situation and not with the testis, if the absence of the spermatogenic function is the result of the malposition, then the operation of Orchidopexy should restore this function. It may be accepted that if an immature imperfectly descended testis is secured within the scrotum without operative injury it will complete its development and function normally.
But if the final stages of spermatogenesis are effected in one situation, the scrotum, and not in another, the abdominal cavity, there must exist some great difference between these two situations.
Such a difference does exist. It is that the temperature within the tunica vaginalis is appreciably lower than that within the general abdominal cavity.
It was known to John Hunter that the temperature of the body is not the same throughout; he demonstrated this fact by several most ingenious experiments on mice and dogs. But more recently, and with much more critical methods, Benedict and Slack have shown that there is a temperature gradient of some 5° C. between the temperature of the abdominal cavity and that of the surface of the body. The temperature rises in proportion to the depth to which the thermometer is inserted until at 6-8 cms. a constant temperature is reached.
The testis within the scrotum is not exposed to the same temperature as that of the primitive position within the abdomen. Moreover, a consideration of the peculiar structure of the scrotum will show that this is a very specialised area of body surface extremely well equipped with a mechanism for local temperature-regulation.
The scrotum is a pouch composed of skin and the dartos tunic. It is divided on its surface by a median raphe into two lateral portions. The skin is very thin, of a brownish colour, and is usually thrown into rugae. It is well supplied with sebaceous follicles, the secretion of which has a peculiar odour, and is beset with thinly scattered crisp hairs, the roots of which are visible through the skin.
F. A. E. Crew 104 The dartos tunic is a thin layer of non-striated muscle, continuous around the base of the scrotum with the two layers of superficial fascia of the groin and of the perineum. It sends inwards a septum which extends between the median raphe and the under surface of the penis, as far as its root, and divides the scrotum into two cavities for the testes. It is closely applied to the skin externally and is connected with the subjacent parts by a delicate areolar tissue upon which it glides with the greatest facility. There is no fat in this areolar tissue; the scrotum is fat-free even in the fattest of entire animals.
But in the castrate the scrotum is loaded with fat and the butcher's test for prime beasts is the amount of fat in the scrotum.
Klaatsch has shown that in many mammals the site of the future scrotum is marked out by a certain area of skin, evident both by its naked-eye and microscopic characters. White and Martin state that in cases of ectopy in which, owing to an over-development of an insertion of the gubernaculum other than the usual, the testis comes to occupy a position beneath the skin of the perineum, the overlying skin assumes the peculiar characters of that of the scrotum.
The appearance of the scrotum varies with different conditions of atmospheric temperature. Under the influence of warmth, and in the debilitated and old, it is elongated and flaccid; under the influence of cold, and in the young and robust, it is short, corrugated, and closely applied to the testes.
The amount of surface exposed is controlled by the action of the dartos.
The scrotum stands well away from the body and is in an area where transpiration is well marked. The temperature within it is not only considerably lower than that within the general cavity but its regulation is controlled by a most efficient mechanism.
That the scrotum itself, by reason of its specialised structure, is concerned in the functioning of the testis is shown by the results of certain diseases in which the scrotal integument becomes very much thickened and inelastic, as in Elephantiasis arabum, for the testes become deformed and atrophied.
The testis within such a scrotum is in a situation equivalent in many ways to the interior of the abdominal cavity.
John Hunter, Ashworth, Child, Marshall, Reamur, Semper, Graham Kerr, Bles, Spallanzani, Meek, Turner, C. L., and many others have produced considerable evidence which goes to show that reproductive activity is intimately related to external temperature in the case of the lower orders. In the fish, for example, it has been shown that the beginning of the annual decline in temperature is contemporaneous with the seasonal volumetric increase in the testes of the Perch, and that the beginning of the seasonal decrease in the testes is contemporaneous with the beginning of the seasonal rise in the temperature. It can be accepted that growth and reproduction vary in length and periodicity with temperature and though, undoubtedly, other factors also are concerned, it is sufficient to recognise that temperature itself is a factor.
Aspermatic Condition of the Imperfectly Descended Testis 105 In the case of the testiconda it is possible that some of the pharyngeal derivatives, such as the thymus, the function of which is not definitely known, control the activities of the testes throughout the individual's whole lifetime, whereas in the case of the mammals whose testes normally migrate to the scrotal position, the action of the internal secretion of this gland has become restricted to inhibiting the too active development of the testis up to the time of puberty, when the body is sufficiently grown so that it can entertain the demands of spermatogenesis. The thymus is so situated that it can readily appreciate changes in the environmental temperature and its intimate association with the activities of the testes is acknowledged. In the case of the scrotal testis, the situation is such that the optimum temperature for spermatogenesis can be maintained throughout the year because of the development of the local temperature-regulating mechanism. The thymus become unnecessary after puberty and consequently atrophies.
But be it as it may, the fact remains that the testes of the testiconda, and of the other Vertebrates in which their normal position is abdominal, have never been required to adapt themselves to function in a situation in which the local temperature is markedly different to that of the general abdominal cavity. This also applies to the ovaries of all the'Vertebrates. They are so organised as to function quite satisfactorily in an intra-abdominal situation, and so far as can be ascertained, should an ovary come to occupy an ectopic position, it does not produce functional ova. This great distinction between ovary and testis in the case of the higher mammals has a very direct bearing upon the question of hermaphroditism in the human and renders the postnatal reversal of the sex-organisation, such as occurs in the case of the Amphibians, for example, utterly impossible.
Since the capacity for functioning within a scrotum has been of the nature of an adaptation, it is not extraordinary that exceptionally an imperfectly descended testis should produce functional spermatozoa.
1. In the more impulsively active mammals the testis leaves its primitive position to pass into the scrotum. The process of migration has been shifted back ontogenetically so that now the formation of the inguinal canal and of the scrotum occurs in anticipation of the descent of the testis. The process bears no great relation to either advantage or disadvantage; it is but the inevitable'concomitant of other constant features of the animal's existence and has not arisen in relation to ulterior ends.
2. The testis has become adapted to function in a situation, the conditions of which are markedly different from those of the general abdominal cavity.
It can no longer function in the primitive position. The great difference between the two situations is one of temperature. The temperature within the tunica vaginalis is considerably lower than that within the abdomen. The scrotum Anatomyr LVX.,Mmtomy LYX 8 106 F. A. E. Crew is so constructed that it is exceedingly well equipped with a temperatureregulating mechanism. The final stages of spermatogenesis occur at a certain optimum temperature which is that within the scrotum and not that within the abdominal cavity.
3. The imperfectly descended testis is aspermatic because the temperature of the abnormal position is not that at which the final stages of spermatogenesis
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