MEMBRANA PROPPJA OF THE ALVEOLI. 467 



that these stellate cells are anything different from the mem- 

 brane. The whole thing constitutes an histological unity ; the 

 stronger longitudinally striated ribs are distinguishable from 

 the matrix of the membrane, but pass quite gradually and 

 imperceptibly into the matrix, which last, usually on both 

 sides of the ribs, becoming gradually fainter, exhibits a longi- 

 tudinal striation parallel to the ribs. 



This description of the structure of the membrana propria, 

 the correctness of which may be easily established by the 

 examination of preparations of glands treated with iodine- 

 serum and teased out with needles, or of sections of glands 

 cautiously hardened in Muller's fluid and brushed out at 

 their free borders, forms a most satisfactory explanation of 

 the extremely various appearances which frequently occur 

 in the same preparation, according to the more or less pro- 

 longed maceration to which it has been subjected, or the 

 greater or less facility with which the tissue breaks down. 

 Owing to these causes, appearances may be obtained from the 

 teasing out of glands macerated in diluted Muller's fluid of a 

 variable and, as it would almost appear, a completely con- 

 tradictory nature. Sometimes isolated alveoli are met with, 

 the epithelial cells of which appear to be contained in a 

 perfectly closed and for the most part strongly wrinkled 

 homogeneous sac; sometimes, on the other hand, there are 

 naked groups of epithelial cells which still preserve the form 

 of the alveoli, and to which a few isolated stellate cells adhere. 

 Then, again, perforated basket-work masses, composed exclu- 

 sively of stellate cells and their processes, float in the fluid, 

 and in the cavities of these a few secretory epithelial cells are 

 usually discoverable. In addition to an innumerable number 

 of isolated gland cells, isolated cells are also to be found of the 

 same kind as those that form the membrana propria. The 

 form and size of these are subject to considerable differences. 

 In young animals (as may best be seen in the Calf) they are of 

 larger size, not only in regard to the central mass, but their pro- 

 cesses are more developed. Each cell is gibbous in form, the 

 centre being sometimes protruded in the form of a vesicle ; and 

 thus, when seen in profile, it often appears like a sickle, which 

 in sections of the hardened gland not unfrequently encircles 



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