VOL. XUI.] PHILOSOPHICAL TRANSACTIONS. 56l 



and by this means the blood is exposed to the air under a prodigious large sur- 

 face, by which the putrefaction is prevented, which, from the alcalescent qua- 

 lity of that fluid, would otherwise be speedily destructive. 



It has been frequently tried, that if a gallon of air be contained in a bladder, 

 and by means of a blow-pipe inspired and expired by the lungs of a man, with- 

 out having any communication with the external air; in the space of a minute, 

 or little more, it becomes heated, and unfit for respiration ; and without the 

 addition of fresh air, the person would speedily be suffocated. The diving-bell 

 is another instance of the same kind, where a constant supply of fresh air must 

 be had, to keep out the water, and refresh the people included. 



Though air is absolutely necessary to our existence, and necessity constrains 

 us inevitably to breathe in it, it may be made a vehicle of most malignant poi- 

 sons ; as the famous Grotto del Cani in Italy, poisoning air by charcoal, air 

 impregnated with the fumes of fermenting vegetable liquors, stagnant air, 

 either alone or mixed with water, soon becomes pernicious and very offensive ; 

 as in wells dug for supply of water, and disused for some time ; also in the wells 

 and in the holds of ships, where what is usually called the bulge-water, if the 

 ship is tight, and the water not pumped out often, it soon becomes so extremely 

 poisonous, as frequently to suffocate those seamen, who, as the putnps are sub- 

 ject to be clogged with filth, venture down to cleanse them; and also to affect 

 persons at a distance with violent head-achs, cold sweats, and frequent vomit- 

 ings, which continue more or less, in proportion to the distance from the well 

 of the ship when the injury was received, and the degree of putrefaction in 

 the water and air. 



The air, in ships particularly, is very liable to be vitiated ; not only from the 

 bulge-water, but from too many people breathing in the same atmosphere; 

 especially in ships of war, hospital ships, and those used in the Guinea trade 

 for negroes, where a number of uncleanly people, being stowed too close toge- 

 ther, heat the air, make it replete with noxious effluvia, destroy the particles 

 adapted to cool the lungs, particularly the acid nitrous gas, which is so abun- 

 dant in cool air, and manifests itself not only by the quantity of nitrous crys- 

 tallizations, which may be collected from caverns of the earth, especially those 

 open to a northerly aspect, but by exposing pieces of the flesh of animals fresh 

 cut, or their blood, by which the colours of their surfaces are soon changed 

 from a dark deep red, to a more lively and florid one. Air deprived of this va- 

 luable property, and replete with hurtful ones, not only from the people, but 

 from the stinking water in the well and lower parts of the ship, must produce 

 the most putrid, if not pestilential fevers. 



Though the equilibrium within places confined is maintained by the external 



VOL. VIII. 4 C 



