92 BIOLOGICAL & CHEMICAL ASPECTS OF SOME ANIMAL NEOPLASMS [Vol. XXI, Part II,
The epidermal origin of melanoblasts was supported by the following morpho-
logical features in cutaneous melanomas: (1) melanoblasts in the upper layers of
the epidermis suggesting the transformation of the epithelial cells to melanoblasts,
(2) the phenomenon of 'Abtrofung' or the downward migration of epidermal
melanoblasts into the dermis and (3) the occurrence of epithelial pearl-like structures.
In melanomas of other organs the presence of dendritic melanoblasts and structures
resembling Wagner-Meissner's corpuscles favoured neurogenesis. Histological
evidences in melanomas studied support the hypothesis that these neoplasms have
more than one origin. The idea is also supported by the fact that melanoblasts
normally occur in entirely different tissues of the body. Twenty-three thyroid
tumors from horses were also studied. They were intraglandular, usually affecting
one lobe and separated from the normal thyroid tissue by a thin fibrous capsule.
No metastases were found. On the basis of histological features the tumors were
classified as adenomas and adenocarcinomas however, their biological behaviour
indicated that all were benign. None of the five sets of transplants of six animals
each, showed growth. Their benign nature was also supported by the absence of
infiltrative tendency and metastasis of the tumors in the primary host.
Carefully selected fragments from 41 fresh animal tissues (25 malignant, 10
embryonic non-neoplastic and 6 benign) were transplanted to the anterior chamber
of 241 guinea pigs. Growth occurred in 13 out of 25 malignant tissues, in 7 out of
10 embryonic non-neoplastic tissues and in none of the 6 benign tissues. All
implants of benign tumors were invariably absorbed within six to nine weeks.
Fifty-two per cent of the histologically diagnosed malignant tumors such as equine
malignant melanoma and renal carcinoma, bovine squamous cell carcinomas, canine
osteogenic sarcoma and seminoma and avian renal carcinoma showed good growths
in heterologous anterior chamber transplants as indicated in Table I.
Malignant tumors did not grow identically in all guinea pigs. These tissue
transplants grew in only 23.7 per cent of the animals. Transplants which grew quickly
regressed early and those which grew slowly regressed slowly. Most neoplastic
tissues grew within two to three weeks after transplantation. In a few cases
growth started on the ninth to twelfth day at the earliest and in
some others a delayed growth occurred by 24 to 29 days after transfer.
Plate V, figs. 1 and 2 presents the above data in detail. All growths
were restricted to the anterior chamber and no instance of metastasis
was found. An ocular reaction to foreign tissue graft usually occurred
but the response was slight or absent to a second transplantation to the same eye.
All transplants which grew invariably regressed after a certain period. Regression
of all transplants was complete within twelve weeks after transfer. A morhpological
survival of about five months without growth or regression occurred in some trans-
plants of equine melanomas and bovine carcinoma after an initial take. Guinea
pigs in which the transplants were absorbed or regressed after growth were as a rule
resistant to second transplantation to the same eye. Exceptions were two avian
renal carcinomas which grew better during second transplantation although the
implants in both transplantations were identical in regard to the type of tumor,
the organ of origin and the species of animal.
The span of life of animal neoplasms transplanted to guinea pig eyes was shorter
than that reported for human neoplasms. A diagnosis of malignancy based on