If the two dissimilar diseases meeting together in the human being be of equal strength, or still more if the older one be the stronger, the new disease will be repelled by the old one from the body and not allowed to affect it. A patient suffering from a severe chronic disease will not be infected by a moderate autumnal dysentery or other epidemic disease. The plague of the Levant, according to Larry,* does not break out where scurvy is prevalent, and persons suffering from eczema are not infected by it.
Rachitis, Jenner alleges, prevents vaccination from taking effect. Those suffering from pulmonary consumption are not liable to be attacked by epidemic fevers of a not very violent character, according to Von Hildenbrand.

* “Memoires et Observations,” in the Description de l’ Egpte, tom. i.