FORMATION OF THE TISSUES. 463 



to be distinguishable. In no instances do such deposits ever undergo further 

 organization; and, therefore, they must be regarded as caco-plaslic. But in 

 the opaque, crude, or yellow Tubercle, we do not find even these traces of 

 definite structure ; for the matter of which it consists is altogether granular, 

 more resembling that which we find in an albuminous coagulum. The larger 

 the proportion of this kind of matter in a tubercular deposit, the more is it 

 prone to soften, whilst the semi-organized tubercle has more tendency to con- 

 traction. This is entirely aplastic. Now although Tubercular matter may be 

 slowly and insidiously deposited, by a kind of degradation of the* ordinary 

 Nutritive process, yet it cannot be doubted that Inflammation has a great ten- 

 dency to favour it ; so that a larger quantity may be produced in the lungs, 

 after a Pneumonia has existed for a day or two, than it would have required 

 years to generate in the previous mode. But the character of the deposit still 

 remains the same ; and its relation to the plastic element of the blood is shown 

 by the interesting fact, of no unfrequent occurrence, that, in a Pneumonia 

 affecting a Tuberculous subject, Plastic Lymph is thrown out in one part, 

 whilst Tubercular matter is deposited in another. Now Inflammation, pro- 

 ducing a rapid deposition of Tubercular matter, is peculiarly liable to arise in 

 organs, which have been previously affected with chronic Tubercular deposits, 

 by an impairment of the process of textural Nutrition ; for these deposits, 

 acting like foreign bodies, may of themselves become sources of irritation ; 

 and the perversion of the structure and functions of the part renders it pecu- 

 liarly susceptible of the influence of external morbific causes. These views, 

 at which several recent Physiologists and Pathologists have arrived on inde- 

 pendent grounds, seem to reconcile or supersede all the discordant opinions 

 which have been upheld at different times regarding the nature of Tubercle ; 

 and lead to the soundest views with respect to the treatment of the Diathesis. 



IX. Formation of the Tissues. 



611. From the primordial cells, of which the whole fabric of the embryo, 

 or the tissue of a newly-formed part, is composed, all the Animal tissues, various 

 as they are in structure and in properties, are gradually elaborated. Their 

 variety is much greater than that which exists in Plants ; and this is exactly 

 what we should expect, when we take into account the much greater number 

 of entirely different functions to be performed. When we contrast the fabric 

 of an Animal with that of a Plant, we are struck with this important dif- 

 ference in their conformation, that whilst the latter is made up solely of ele- 

 ments which are to perform their several parts in the performance of the 

 Nutritive and Reproductive operations (the only exception being in the case of 

 those more solid portions of the fabric, which are destined to give mechanical 

 support to the remainder), the former is composed of a much greater variety 

 of parts, which are adapted to move upon each other. Now this purpose 

 requires, not only the addition of certain new tissues, to which nothing ana- 

 logous is to be found in Plants, for creating and exercising the motor power, 

 but also an adaptation of the whole structure to this new condition. The tissues 

 of Plants entirely consist of cells, or simple modifications of them. Some of 

 these cells being strengthened by internal deposits, form the solid woody frame- 

 work of the stem and branches ; which gives support to their wide-sprsading 

 foliage and numberless blossoms. Others coalesce, by the disappearance of 

 their intervening partitions into tubes ; which serve for the conveyance of fluid 

 between the most distant parts. But the great bulk of the fabric still consists 

 of cells, closely adherent to each other, and actively participating in the various 

 operations of organic life. In like manner, in the Animal body, a certain part 

 of the cells have contributed to form the solid Osseous and Cartilaginous frame- 

 work, which not only gives support and protection to the body, but contributes 



