in all appearance, more or less to a suppression of the
circulation of air and blood by the black substance. His impression is,
"that the carbon is not procured from without, but naturally deposited,
as life advances, in the substance of the respiratory organs; and that
this deposit of carbon causes death, by rendering the lungs
irrespirable, while, at the same time, it has much influence in
modifying the progress of _tubercular_ disease; so that, if the
tubercular affection was not cured, its progress was so far checked,
that life has been very long preserved." The black matter envelopes
completely both the pulmonary tubercles which have undergone a
transformation, and the caverns which no longer contain tuberculous
matter. He, while regarding these as the results of black matter in the
lungs, throws no light on the cause of the deposit of the particles of
carbon within the lungs.

Dr William Craig of Glasgow, in a letter to Mr Graham of London,
published in the 42d vol. of the _Medical and Surgical Journal of
Edinburgh_, states most interesting facts connected with this subject,
particularly in regard to black matter found in the pulmonary structure
of old people, which deserve considerable attention. He says--"I found
that a black discoloration of the lungs was by no means a rare
occurrence amongst those old people; and that it was impossible in many
instances to decide, whether the black colour was owing to an increase
of what is called the healthy black matter,--to a morbid secretion, or
to a foreign substance being imbedded with the atmospheric air. After
examining a considerable number of lungs, and finding that the division
of the black matter into three kinds was not founded upon observation,
and that the descriptions of them given by the best authorities were
insufficient to enable us to distinguish them from one another, I begin
to think, that in every instance in which black matter is found in the
lungs, it ought to be considered morbid. If we examine the lungs at
different stages of life, we find as a general rule that the quantity of
black matter increases with age. In young children we find no traces of
it, the lungs being of a reddish colour. At the age of ten years the
black matter makes its appearance in the outer surface of the lungs, and
in the interlobular spaces. At the age of thirty or forty, the lung
presents a greyish or mottled appearance, and the bronchial glands
contain more or less black ma