236 PARALYSIS OF SECT. XXVIIl. 2 . 



ducing he&ic fever ; but as focn as the wound is opened, fo as 

 to admit air to the furface of the ulcer, a hedlic 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 oxy- 

 gene ; becaufe thofe medicines, which contain much oxygene, 

 as the calces or oxydes of metals, externally applied* greatly 

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

 mercury, and copper in acids, or their precipitates ; but have 

 fince believed it owing to the oxygene. See Clafs II. i. 6. 7. 

 in Vol. II. of this work. 



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

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

 them. Hence we have one caufe, which prevents pulmonary 

 ulcers from healing, which is their being perpetually expofcd to 

 the air. 



Another caufe of the difficulty of healing pulmonary ulcers 

 may arife from the inactivity of the veflelsof 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 (kin. For it is probable, that the air-cells alone of the 

 lungs conftitutethe 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 

 Surfaces of the pulmonary veffels, which lead to them Hence 

 the mucus, which in common coughs or fuperficial peripneumo- 

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

 is forced up in coughing ^by the air behind it, which ishaftily 

 excluded from the air-cells, and flowly inhaled into them. But 

 if there was any mucus or matter formed in thefe air-cells, it is 

 not eafy 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 exift 

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

 veflels leading to the air-cells, as after a wound with a fword, 

 or when a vomica has burft after a peripneumony. 



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

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

 piration, and M. Bonnet in his Ufage des Feuilles (hows by a 

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

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

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

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

 the under furfaces of many others of them - 9 and he uniformly 



founci 



