The pustules develop from the Papular layer of the skin, and contain a yellowish-white pus.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
M. Michel states that the spores from the parasite on Arundo donax, either inhaled or injected, produce violent Papular eruption on the face, attended with great swelling, and a variety of alarming symptoms which it is unnecessary to particularize, in various parts of the body.
"Fungi: Their Nature and Uses"
Mordecai Cubitt Cooke