If the older disease is the same strength or stronger, it will fend off the new one.
i. If two dissimilar diseases meet together in the human being and they are either of equal strength, or the older one happens to be stronger, then the older disease will keep the new one away from the body.
Severe chronic diseases fend off moderate epidemic ones.
1. Someone who is already suffering from a serious chronic disease will not be infected by an autumnal dysentery or other moderate epidemic disease.
Scurvy fends off the plague.
2. The levantine plague does not break out where scurvy reigns, according to Larrey. 76
Eczema fends off the plague.
3. People suffering from eczema are also not infected by the levantine plague, according to Larrey. 77
Rachitis fends off smallpox vaccination.
4. Richitis prevents smallpox vaccination from taking effect, according to Jenner.
Pulmonary tuberculosis fends off moderate epidemic fevers.
5. People with ulcerous pulmonary tuberculosis are not infected by epidemic fevers that are less severe, according to von Hildenbrand.
76 Larrey, «Mйmoires et observations,» in Dйscription de l’Egypte [«Reminiscences and observations,» in Description of Egypt], vol. I.