2 3 5 PARALYSIS OF Sect. XXVIII. 2, 



ducing hectic fever ; but as foon as the wound is opened, fo as 

 to admit air to the furface of the ulcer, a hectic fever fupervenes, 

 even in very few hours, which I formerly conceived to be owing 

 to the azotic part of the atmofphere rather than to the oxygene ; 

 becaufe thofe medicines, which contain much oxygene, as the 

 calces or oxydes of metals, externally, applied, greatly contribute 

 to heal ulcers; of thefe are the folutions of lead, and mercury, 

 and copper in acids, or their precipitates ; but have fince believed 

 it to be owing to the oxygene. See Clafs II. 1. 6. 7. in Vol. II. 

 of this wor] . 



Hence when wounds are to be healed by the fird intention, 

 as it ir> called, it is neceflary carefully to exclude the air from 

 them. Hence we have one caufe, which prevents pulmonary ul- 

 cers from healing, which is their being perpetually expofed to the 

 air. 



Another caufe of the difficulty of healing pulmonary ulcers 

 may arife from the inactivity of the veflels of the air-cells, which 

 are covered with a membrane differing both from that of the mu- 

 cous membranes of other cavities of the body, and from the ex- 

 ternal fkin. For it is probable, that the air-cells alone of the 

 lungs conflitute the organ of refpiration, and not the internal fur- 

 faces of the branching vefTels of the trachea which lead to the 

 air-cells. And from a vegetable analogy mentioned below they 

 probably exhale or perfpire either nothing or much lefs than the 

 furfaces of the pulmonary vefTels, which lead »to them. Hence 

 the mucus, which in common coughs or fuperficial peripneumo- 

 ny is fecreted on the fnrface of the branching vefTels of the lungs, 

 is forced up in coughing by the air behind it, which is haitily ex- 

 cluded from the air-cells, and flowlv inhaled into them. But if 

 there was any mucus or matter formed in thefe air-cells, it is not 

 cafy to underftand how it could be brought up by coughing, as; 

 no air could get admittance behind it ; which may be one caufe 

 of the difficulty of healing pulmonary ulcers if they exifl on the 

 furface of the air-cells ; but not fo, if they exift in the vefTels: 

 leading to the air-cells, as after a wound with a lword, or when 

 a vomica has burft after a peripneumony. 



In the vegetable fyflem, I think, there can be no doubt, but 

 that the upper furface of the leaves conftitutes the organ of res- 

 piration, and M. Bonnet in his Ufage des Feuilles mows by 3 

 curious experiment, that the upper furfaces of leaves do not ex- 

 hale half lb much as their under furfaces. He placed the ftalks 

 of many leaves frefh collected into glafs-tubes filled with water, 

 of many of thefe the upper furfaces were fmeared with oil, and 

 ihe under furfaces of many others of them ; and he uniformly 



found 



