282 THEORY AND PRACTICE OF MEDICINE.
the breath and exhalations, but there is no adequate foundation for such a notion. Nor is there any reason to suppose that the disease is transmitted by vaccination, as has been alleged. _ Recent- ly experiments have been made which have given origin to the view, that tubercular disease can be transmitted by eating the flesh of animals affected with this complaint, and that this may be the cause of many cases of phthisis, but for such a view the evidence must be much more conclusive before it can be accepted.
The immediate causation of the formation of tubercle will be discussed under the head of pathology.
Anatomical Characters. — General description. The typical variety of true tubercle almost universally recognized at the pre- sent day consists of certain minute bodies, termed grey granulations or miliary iiihetclcs. 1 hese appear as small nodules or granulations, about the size of a mustard or millet-seed ; generally of a roundish form, but sometimes slightly angular; well-defined; usually firm, but occasionally soft; of a greyish-white or pearly-grey colour; more or less translucent; and non-vascular. These may be quite sepa- rate and distinct ; or collected into irregular groups, their individual outline being then rendered indistinct. In some structures, however, tubercle is more diffused, and appears as a greyish infiltraiion,c presents a smooth and dense section ; but many so-called tubercu- lar infiltrations are probably inflammatory in their origin. In its earlier stage tubercle is not visible to the naked eye, and it is by the continued growth and agglomeration of fresh tubercles that it becomes perceptible, appearing either as granulations or infiltra- tions according to their mode of arrangement.
What has been described as yelloio tubercle is nothing but nodules or masses of caseous matter, derived either from tubercle, or from various inflammatory and other morbid materials which have un- dergone cheesy degeneration. True tubercle may be mixed with this material ; while it also tends to excite inflammation around, and thus its physical characters may be more or less modified.
Microscopic structure. — Tubercle may be described as consist- ing of more or less of the following histological elements: — i.
 | An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|A Handbook of the Theory and Practice of Medicine - Volume I - Frederick T. Roberts.djvu/298}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. |  |
Lymphoid coipuscles, which are very small, round, colourless, translucent, and slightly granular, each containing" a single nucleus. 2. Epithelioid cells, of larg'er size, very deli- cate, and hence liable to rupture and to set their nuclei free. 3. A giant-cell, which consists of a mass of finely-granular proto- plasm of very varied form, often presenting processes at its margin, and having im- bedded in it a great number of round or roundly-oval nuclei, usually collected chiefly at its periphery, and sometimes regularly arranged, each containing" one or some- times two bright nucleoli. 4. Free nuclei. 5. An intercellular substance, which may be either amorphous, homogeneous, and hyaline; or granular; or in the form of a fine reticulum or
Fig. 10.
Elements from grey tubercle miliary granulation. {Jones and Sicvcking).
