170 Dr. Pearson on the colouring Matter, &c. 



black lines, supposed to be a lymphatic vessel. Being put 

 into a glass capsule, full of nitric acid, the black line imme- 

 diately was contracted in all dimensions ; but it retained its 

 form after digestion, for several days, at a high temperature: 

 afterwards on gently shaking the .capsule, the black hne was 

 broken into a number of indissoluble particles. In the interior 

 of the lungs, it is not unusual to see black spots in the middle 

 of tubercles, although these substances consist apparently of 

 self-coagulated lymph probably secreted in the cellular sub- 

 stance, and therefore very likely to envelope the coaly matter 

 in the air tubes by the coalescence of numerous minute tu- 

 bercles. 



It has been objected, that the nitric acid may develope the 

 constituent or combined ingredient charcoal of all animal sub- 

 stances ; and consequently no proof will be thereby afforded 

 of this matter being extraneous; but on many trials, I have 

 never by this means obtained charcoal from any animal muci- 

 lage. 



I have no reason to believe, that any of the coaly matter 

 under investigation, is dissolved by this acid, for on distilling 

 a pint measure of it, from ten grains of the black powder of 

 the bronchial glands, there was no sensible diminution of it, 

 whether it was so treated before ignition, or subsequently: on 

 evaporation to dryness, nitric acid, in which the coaly matter 

 had been boiled, afforded no black sediment. Hence, I con- 

 ceive, that this menstruum may be employed to determine, 

 more accurately and speedily, the proportion of the coaly 

 matter, than any other agent. Sulphuric acid does dissolve a 

 certain portion of this charcoal, affording a transparent liquid, 

 even on dilution with water. 



