i6o Dr. Pearson on the colouring Matter 



the air may be the occasion of the colour of the lungs ; and 

 that the colour of the glands is occasioned by a peculiar secre- 

 tion. But the former conjecture has been supposed to be 

 satisfactorily refuted by the absence of the appearance in 

 question among brute animal§ ; as also by its presence in per- 

 sons who breathe the air of the provinces at a great distance 

 from towns, or places of great consumption of coal ; and the 

 latter conjecture is palpably erroneous, because the bronchial 

 glands, of which I am speaking, are not organs of secretion, 

 but of conveyance of lymph. 



The course of investigation, in which I have long been en- 

 gaged, to improve the pathology of pulmonary consumption, 

 led me to some experiments and observations on the subject 

 now stated, which I respectfully submit to the consideration 

 of the Society. 



After cutting away the cellular membrane surrounding the 

 black glands, and washing them till the water was no longer 

 coloured, I subjected them to examination. 



1. On pressure between the fingers, to burst the investing 

 coat, a black fluid issued which stained the skin, which ren- 

 dered water black, and which did not alter in colour or appa- 

 rently dissolve, even at a boiling temperature, either in water 

 or in concentrated muriatic and nitric acids. 



2. On breaking down the structure and triturating in a 

 glass mortar a number of these glands with a small proportion 

 of water, a thick black liquid was produced, which was decanted 

 from off many membranous and fibrous masses. But after 



•^repeated affusions and trituration, I could not derive these 

 masses of their black colour, although the water was at last 

 scarcely tinged : it was only by dissolution in caustic pptash 



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