This document explains the progression of Leonard's mutation as a result of injecting himself with the anti-aging serum, and his exposure to the light. It's found in Friedman's underground lab.
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January 18, 1903
Leonard seems to have handled the treatment
reasonably well. No special symptoms.
March 24, 1903
After a few days his skin is covered with melanoma.
The tumors are not metastasizing very much, but
their large number is causing a worsening in his
general condition.
March 30, 1903
The hypersensitivity of the skin to UV radiation and
the first lesions resulting from this are similar to
Xeroderma Pigmentosum[1], an inherited illness. This
illness is due to a mutation of the gene that protects
against skin cancers. But, in theory, this illness is
hereditary.
April 18, 1903
Henceforth, Leonard will protect himself from the
sun, but the damage is done. The light rays have
caused an acute reaction in the Mortifilia gene inserted
into his system. We did not foresee this, because our
previous guinea pigs remained in their cages. At present
the entire surface of Leonard's skin is suffering profound
mutations.
May 25, 1903
The mutations appear to have slowed down. They are,
however, spectacular, and I ask myself how he can
survive in this condition. The wounds have transformed
into scabs that look as though they will remain, like the
bark of a tree. The damage to his skeleton and his
metabolism appear irreversible. His temporal lobes and
his upper members are the most affected parts.
June 30, 1904
His condition has stabilized. His mental condition
concerns me as much as the appearance he has taken on,
if human appearance can still be spoken of in his case.
The only hope to cure him now is to have new guinea
pigs who have suffered in the same way, in order to test a
therapy aimed at eradicating the gene and returning the
subject to his initial condition.
September 24, 1926
This research is very long. I will not live long enough to
achieve my goal. Unless I inject myself with the treatment
and remain in the shadows until the serum is discovered.