M. Y.
MANGRULKAR
181
tissue of the affected site reveals an early reaction
sufficient to be recognized as a true stroma.
Microscopically, the stages between the benign
and malignant melanomata can often be seen.
Suitable material will also illustrate the possibility
that under unknown circumstances a benign-
looking neoplasm may assume malignant charac-
ters. Both types of melanoblast may co-exist in
the same microscopic field or in different parts of
the same section, suggesting a proliferative
tendency supervening on the essentially primary
function of pigment-production.
The tumours may attain large dimension and
vary in consistency from fluid or pulpy to
hard; accordingly, on incision, the amount and
nature of the escaping pigment varies. Portions
of melanotic tumours kept in commonly used
fixatives often impart the melanin tinge to the
preservative. Superficial tumours are likely to
ulcerate and discharge a dark-pigmented, foul-
smelling fluid (79/1934). Rarely, the formation
of the pigment may be so excessive that it may
appear in the blood stream (melanaemia) in the
urine (melanuria) or in various other situations
(melanosis). The primary or metastic tumours in
the serous cavities may be responsible for the
presence in these cavities of pigmented fluid, some-
times amounting to several gallons.
In the horse, the cutaneous tumours are
nodular, plain or elevated, occasionally pedun-
culated growths covered with skin. The tumours
in the internal organs are generally looked upon
as metastases of a known or undetected primary
skin-tumour. According to some [Ewing, 1934],
primary melanomata, especially in man, may
grow in these situations, owing to the misplace-
ment of melanoblasts during development.
It should not be understood that horses other
than grey are immune from melanomatosis, for
veterinarians do occasionally encounter such
cases.
Few cases of melanomata in mules have
been recorded. In the collection at this Insti-
tute, there is material from five cases, but gene-
ralization is not possible on the strength of such
meagre data. Of the five, four were accompanied
by details regarding colour and age; three were
from grey aged 8, 15 and 18 years, the fourth being
from a 10 year-old brown animal. All four speci-
mens were malignant tumours, which fact is in
conformity with the observations of other workers
[Aubry, cited by Feldman, 1932; Mathews, 1929;
Frank and Morrill, 1937].
Unlike what occurs in the horse, the perineum
and tail in mules do not seem to be the common
sites of primary melanomata. The tumours in
our collection affected the deeper tissues of the
shoulder and thigh region, the organs and wall
of the thorax and the abdomen, and in one
case the mammary gland. It would appear
that, whereas in the horse the apparently benign
and superficial tumours are the first to attract
attention, in mules early malignancy with the
involvement of the internal organs is frequent.
Indeed, in these animals, numerous metastatic
growth may be discovered in the internal
organs at autopsy, and the primary growth
may have escaped detection during life.
In one of the cases in our collection (1116/1927),
it was suspected that a kick had been responsible
for provoking a primary tumour in the sheath,
discovered and interpreted as such on autopsy, to
malignancy and internal metastasis, causing death
within three months.
The three specimens of bovine melanomata in
our collection came from the skin of the chest,
scrotum and pastern and were clinically benign
and operable. In one of them (958/1926), the
skin showed the evidence of filariasis (Plate XV,
fig. 4), but what relation, if any, this had with the
presence of the melanoma is open to conjecture.
The tumours were nodular, hard and more or less
deeply pigmented masses. One of them was peduncu-
lated. There seems to be no age or colour pre-
disposition to melanomatosis in bovines, although
Imminger [cit. Feldman, 1932] has observed the
occurrence of melanotic tumours more frequently
in albino than in dark cattle. Malignant mela-
nomata are rarely found in bovines, (vide
specimen No. 115/1938, Addendum). Unlike
melanomata, melanosis, i.e. mere dark brown or
black pigmentation of the tissues or organs with-
out any material dysfunction of the parts or of the
organ, is relatively more common in cattle.
In calves, melanosis of the cutis (melanosis
maculosa) is seen; this, unlike the congenital
naevi of man, tends to disappear with age
(Feldman, 1932].
Although not represented in our collection,
melanomata also occur in animals other than
equines and bovines. In swine, apart from patchy
benign melanosis of the skin, the occurrence of
melanomata, often malignant with widespread
metastases, has been noted, the primary lesion
appearing usually in or under the skin, not
infrequently when the animal is only a few weeks
old. It is suspected that in certain breeds here-
dity plays a part [Caylor and Schlotthauer,
1926]. The tumours in adult swine are usually
benign.
The dog, like the pig, is also subject to melano-
matosis as well as simple melanosis. According
to Gray [1900] certain breeds of dog, particularly
the Yorkshire terrier, are predisposed to the for-
mer, the tumours being of the nature of cutaneous
elevations, or of single, stalked or sessile smooth