332 



SEROUS 3IEMBIIANES. 



tlie epithelial lai/er of the serous membranes. Nothing hmders 

 them indeed from spreading afterwards, not only into the paren- 

 chyma of the serous membrane, but also through the parenchyma 

 into neighbouring organs. Wherever connective tissue exists, a 

 path is open to them. We must not forget however, that the 

 epitheha of serous membranes are themselves connective-tissue 

 corpuscles. 



§ 284. One example will suffice to illustrate this highly 

 peculiar mode of origin. I choose a miliary tubercle on the 

 omentum. Fig. 107 represents a very small nodule (under a 

 lo^v power), which has not yet grown out of the limits of its 

 birthplace. It consists of a globular aggregate of cells, suspended 

 from nine slender threads of connective tissue radiating 

 from its periphery to the stouter and partly vascular trabecula3 

 Avhich form the boundaries of one of the larger meshes of the 

 omentum. 



Let us examine one of the nine points at which the con- 

 nective-tissue fibres join the nodule, under a higher power, 

 (X 800). Here, at the edge of the formation, we may expect, 

 if the nodule is still growing, to find a^^pear- 

 ances which w^ill shed light u]3on the details of 

 its origin. We find what is represented in fig. 

 108. The nodule grows by proliferation of the 

 epithelial cells. The homogeneous lamella is 

 raised from its bed on one side of the thread of 

 connective tissue, while on the other, it has 

 been shed altogether ; the place of the nucleated 

 protoplasm is taken by larger and smaller groups 

 of young cells, which have clearly sprung 

 from it by a process of fission. The substance 

 of the thread itself is unaltered up to the very 

 edge of the nodule. Here it escapes our obser- 

 vation; but in the interior of the nodule it is 

 still connected with the other eight threads in 

 precisely the same way as it was before the 

 iiy ^'oliferation gi'owth of the tubercle. It obviously takes no 

 of the serous part in the proliferation ; and up to this point 

 ImcIi). ^^' ^^' ^^® ^^'® entitled to regard the whole of the new 

 growth as a product of the serous epithelia. 

 Should the centrifugal growth, at a later stage of its progress. 



Fig. 108. 



X'"^ ^ 



^^ 



Origin of a mi- 

 liary tubercle 



