Arnald also revived the search for some anaesthetic that would produce insensibility to pain in surgical operations.

This idea was not original with him, for since very early times physicians had attempted to discover such an anaesthetic, and even so early a writer as Herodotus tells how the Scythians, by inhalation of the vapors of some kind of hemp, produced complete insensibility.

It may have been these writings that stimulated Arnald to search for such an anaesthetic.

In a book usually credited to him, medicines are named and methods of administration described which will make the patient insensible to pain, so that "he may be cut and feel nothing, as though he were dead." For this purpose a mixture of opium, mandragora, and henbane is to be used.

This mixture was held at the patient's nostrils much as ether and chloroform are administered by the modern surgeon.