244 DISEASES CLASS II. i. 6. 6. 



creases the acrimony of the purulent matter, and even converts 

 it into a weaker kind of contagious matter; that is, to a mate- 

 rial inducing fever. This was ascribed to the union of the azotic 

 part of the atmosphere with the effused pus in Sect. XXVIII. 2. 

 but by contemplating more numerous facts and analogies, I am 

 now induced to believe, that it is by the union of oxygen with it; 

 first, because oxygen so greedily unites with other animal substan- 

 ces, as the blood, that it will pass through a moist bladder to com- 

 bine with it, according to the experiment of Dr. Priestley. Se- 

 condly, because the poisons of venomous creatures are supposed 

 to be acids of different kinds, and are probably formed by the 

 contact of air after their secretion. And lastly, because the con- 

 tagious matter from other ulcers, as in itch, or small-pox, is form- 

 ed on external membranes, and are probably combinations of 

 animal matter and oxygen, producing other new acids. 



Since having written the above, Dr. Mitchell, of New- York, 

 has spoken much of the septic quality of azote, or nitrogen; and 

 thinks that it is the union of this part of the atmosphere with 

 the matter of ulcers, which produces or increases its contagious 

 or fever-exciting property: which I had myself at first believed, 

 as mentioned in Fart 1. Sect. XXVIII. 2. In support of this 

 opinion, it may be said, that proper ventilation with purer air is 

 believed certainly to diminish or destroy infection; as spoken of 

 in Class II. 1. 3. where it is proposed to disengage oxygen from 

 manganese, for the purpose of purifying crowded apartments. 

 But further experiments must determine this curious inquiry; 

 -which might be attended with important consequences, if azote, 

 and not oxygen, could be shewn to prevent the healing of pul- 

 monary ulcers; as oxygen might be respired alone, or mixed 

 with hydrogen or with carbonic acid gas, instead of with azote. 



It was thought a subject of consequence by the ^sculapian 

 Society at Edinburgh, to find a criterion which should distin- 

 guish pus from mucus, for the purpose of more certainly dis- 

 covering the presence of ulcers in pulmonary diseases, *or in 

 the urinary passages. For this purpose that society offered 

 their first gold medal, which was conferred on the late Mr. 

 Charles Darwin, in the year 1778, for his experiments on this 

 subject. From which he deduces the following conclusions : 



" 1 . Pus and mucus are both soluble in the vitriolic acid, 

 though in very different proportions, pus being much the less 

 soluble. 



" 2. The addition of water to either of these compounds de- 

 composes it; the mucus thus separated, either swims on the mix- 

 ture, or forms large flocci in it; whereas the pus falls to the 

 bottom, and forms on agitation a uniform turbid mixture. 



