contagium

noun

1. (archaic)contagion; contagious matter

   “And its escape [from certain diseases] is an approximative proof that, at least for those ten years, no contagium of measles, “nor any contagium of scarlet fever, nor any contagium of small-pox, had arisen spontaneously" within its limits.”

   “That this in fact was the case was ascertained by Dr. Edington, who, by adding a large percentage (33 per cent.) of glycerine to the gall taken from a rinderpest beast, was able to show that by such contact the infective power of bile was as effectually destroyed as was the contagium of blood.”