Etiology

If we may judge from Holy Writ, the ancient Jewish lawgivers regarded the disease as contagious. Modern science declares that it is not. The discovery in recent times of a peculiar bacillus by Hansen gives a clue to the medium of contagion, and corroborates the results of care­ful clinical observation. While we cannot doubt the pos­sibility of contagion, we must admit that within the tem­perate zones the direct transfer of the disease from one person to another has been very rarely observed. It is by no means unusual for a Caucasian to contract the disease when dwelling among the natives where it is endemic; but it is extremely rare for him, on returning to his native country, to convey the malady to those with whom he asso­ciates. During the past several years there have been a large number of lepers who have passed months and sometimes years in the hospitals of New York, and yet not a single case of leprosy has developed in this city. Fox says: "The causes of propagation are mainly these:

1. Intermarriage of the leprous or with the leprous.
2. Hereditary transmission.
3. Inoculation and cohabitation.
4. Vaccination (?).
   

As to intermarriage, little need be said. It sufficiently accounts for the occurrence of a large number of cases of leprosy in the offspring of lepers, and the continuous intermarriage of people of the same caste in India, enforced rigidly by custom and superstition, tends greatly to the spread of leprosy hereditarily.

Secondly - As regards hereditary influence, this is most marked in children who are begotten by lepers far advanced in the disease.

Thirdly. - As to cohabitation and inoculation. Of course, these are not such potent causes as intermarriage and hereditary tendency in spreading leprosy, but still it is probable that they may account for a certain number of cases.

It has been said that leprosy may be communicated by vaccination, but if so it must be infinitely rare and scarcely worthy of being taken into account.