cess bears to suppuration. When Mr. Simon's experiments on the production of tubercle in the rabbit were discussed at the Pathological Society in the spring of 1867, my opinion was asked whether the experiments did not prove the specific nature of tubercle. My reply was in the negative; and that I believed it would be found that tuberculisation bore more analogy to suppuration; and that acute tuberculosis had its parallel in pyæmia. But it is not healthy pus, or other sthenic inflammatory products, which surely produce tuberculosis, but the pus of pyæmia, foul pus, putrid muscle, and such septic matters as must be injurious to the vitality of the bioplasm; these have the same effect as tubercle itself, and the kindred forms of deteriorated bioplasm found in chronic condensations and caseations of the lung, lardaceous liver, &c.

The occasional production of tubercles from more healthy materials, and from the wound of a seton, must be referred to some additional septic influence accidentally acquired, and giving a foulness to the material or to the wound; and here we can perceive how atmospheric hygienic agencies may operate, as in acute suppuration infecting the blood by pyæmia, so in chronic injuries infecting the lymph and blood with tubercle. On this point the following observations of Dr. Burdon Sanderson. are very important, and call for further investigation.

'With reference to the traumatic origin of tuberculosis in the guinea-pig, another possibility claims consideration, namely, that of the influence of the air and of the organisms which it contains. It has not yet been proved that injuries which are of such a nature that air is completely excluded from contact with the injured part are capable of originating a tuberculous process. The following experimental results seem, indeed, to suggest that they may not be so. Setons, steeped in carbolic acid, were inserted in ten guinea-pigs, on September 24, 1868,

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each animal receiving two. At the same time, extensive fractures of both scapula were produced in five others, care being taken not to injure the integument. No tuberculosis or other disease of internal organs has resulted in either case.'1

1

Before noticing some of the details of the process of artificial tuberculisation, I must again advert to the subject of the very different degree of susceptibility shown by different animals. Rabbits and guinea-pigs have been generally selected as affording the most frequent results, and therefore must be considered to be somehow predisposed to artificial tuberculisation, although Dr. Sanderson declares that they are not liable to the natural disease. Attempts made to produce tubercle in other animalsdogs, cats, goats, sheep, and birds-have rarely succeeded. Again, Dr. Fox has remarked that tuberculisation succeeds better with guinea-pigs than with rabbits; and ascribes M. Villemin's repeated failures with other materials than tubercle to his using the latter animals. In several of these experiments the rabbits died of pyæmia, before there was time to produce the more chronic result, tuberculisation; and in others, a local suppuration occurred, without being followed by any appearance of tubercle in the organs. In others, there was a slight appearance of pus, often offensive and becoming cheesy, and this was more generally followed by tuberculisation.

Drs. Sanderson and Fox have given the most complete and minute descriptions of the process of artificial tuberculisation in the guinea-pig, and these should be carefully studied. We can here give only a brief abstract of the principal points, chiefly relating to the primary local effects, and to those in the lymphatic glands and the lungs. The most common result of the introduction of the

'Further Report on the Inoculability and Development of Tubercle,' Eleventh Report of the Medical Officer of the Privy Council, 1869, p. 92.

matter under the skin is the formation of masses of cheesy matter, which are dry and friable ('débris of fattily degenerated material') and often encapsuled. But in addition to these are small granulations, varying in size from that of a poppy seed to that of a hemp seed, irregularly scattered in the subcutaneous tissue. These masses, sometimes transparent throughout, sometimes opaque in the centre, present to the naked eye and under the microscope a striking resemblance to the changed lymphatic glands. In their denser and more central parts they consist of nuclei imbedded in a homogenous tissue; in their less dense parts a fibrillated tissue which forms bands or trabeculæ, between which the cells lie, the whole forming a structure which has the strongest resemblance to the elementary composition of a lymphatic gland. Throughout the granulations many of the cells and also of the nuclei are seen in various stages of fatty degeneration.'

Dr. Sanderson also describes the local effect of the inoculation in the guinea-pig to consist in the production of smail subcutaneous knots, which at first appear to be composed of round cells, like lymph corpuscles (sarcophytes). At a later period these cells are enclosed in a meshwork of fibres, thicker and coarser than the reticulum of a healthy lymphatic gland, but so exactly 'resembling that of a gland enlarged and hardened by disease, that the two are indistinguishable under the microscope.'

According to Dr. Sanderson, the first step in the dissemination of tubercle consists in its being absorbed primarily by the lymphatics (which convey it to the lymphatic glands of which they are tributaries), and secondarily by the veins. Having thus entered the systemic circulation, it is distributed universally by the arteries. The serous membranes seem, however, by preference to

Dr. Wilson Fox, op. cit., p. 8.

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appropriate it, and from them it extends by contiguity to the superficial parts of the organs which they cover."1

Of lymphatic glands, those supplied from the inoculated part may soon become enlarged and congested, with such an enormous multiplication of corpuscles as to impair the consistence of the gland, and sometimes to run into suppuration. When more slowly affected, they enlarge, harden, and caseate. The enlargement is chiefly from multiplication of cells, the induration partly from the same cause (why not from their hardening also ?), and partly from the rapid growth of their fibrous reticulum, or trabecular stroma. The caseation is from fatty decay and disintegration of the indurated mass.

The internal lymphatic glands are affected in consequence of secondary production of disease in the organs from which they receive their afferent lymphatics. Their change is also chronic, and tends never to suppuration, but to enlargement, induration and caseation, referable to the same increased cell formation with fibrous degeneration, and eventual fatty or calcareous necrobiosis. Very similar changes affect the spleen, the structure of which bears a close analogy to that of lymphatic glands.

In Dr. Fox's observations, the lungs were affected with tubercle in fifty-nine cases out of sixty-four-the same proportion as in those invading the spleen. The following is an abridgment of his description :-The chief state I have to describe consists in the lungs being permeated more or less thickly by scattered granulations, varying in size from a millet seed to a hemp seed.' Some are hardly visible specks, and all gradations can be found between the smaller and the larger. Generally they are scattered, but sometimes confluent in groups; even in the larger groups there is evidence that they have been originally composed of distinct granulations. The granulations do Loc. cit. p. 117.

not project much from the cut surface, and they blend more or less intimately with the surrounding pulmonary tissue, from which they tear with difficulty. They are firm, and all marked by a peculiar semi-transparent, hyaline, cartilaginous looking margin, and a cheesy centre, which is sometimes soft in the larger ones, and when evacuated leaves a cavity. Some of the smallest are semi-transparent throughout. They are more common

on the pleural surface than deep in the lung, but are distributed pretty equally through the lobes. Sometimes when there is a group of these granulations clustered together, an appearance is presented, which is also occasionally seen in the human lung, of a fibrous network running between the granules, as if the intervening tissue was becoming fibrous. In addition to this there is a general induration of the lung tissue, affecting in a variable degree the whole organ. Signs of pneumonia and of general infiltration, independent of the granulations, is exceedingly rare.

The microscopic examination of these growths in the lungs presents the following features:-There are three main points in which they appear to originate-around the bronchi, around the blood-vessels, and in the lung tissue unconnected with either. Around the bronchi they seem to extend from little masses of a lymphatic character (adenoid tissue), which normally exist in the bronchial sheath, and are also stated by Kölliker to exist in the human lung. These granulations around the bronchi consist of masses of cells 1-2500 to 1-3000th of an inch in diameter, mostly round; but sometimes, when densely packed, showing nothing but nuclei.' 'In the perivascular sheath of the pulmonary arteries, the growth is nothing more than an accumulation of the cells lining the perivascular canal. The growth may extend for a considerable distance in length along both peribronchial and