466 THE LACHRYMAL GLANDS, BY FRANZ BOLL. 



and Horse, belong to the second kind. In the parenchyma of 

 these glands not a single cell that has undergone mucous 

 degeneration can be demonstrated. It may therefore be con- 

 cluded with certainty that the secretion of the lachrymal 

 glands never contains mucin.* 



According to the researches of Heidenhain, the so-called 

 lunula, first described by Giannuzzi, is formed by a collection 

 of protoplasmatic cells, usually appearing sickle-shaped on 

 section, which are perhaps destined to supply the glandular 

 epithelium that undergoes the mucous metamorphosis. It is 

 obvious that as the lunula is only present in glands in which 

 a mucous degeneration of the secretory elements occurs, we 

 coukl not expect to meet with a lunula in the lachrymal 

 gland, the cells of which, like the epithelial cells of the sub- 

 maxillary gland of the Rabbit, remain permanently proto- 

 plasmic. 



The alveoli are invested by a fine membrane, the so-called 

 membrana propria, the structure of which is very peculiar. It 

 is alwaj^s composed of flat stellate cells, which frequently inter- 

 communicate by means of their often very largely developed 

 processes, that run round the alveoli like hoops. These finely 

 striated, more or less slender or broad processes which constantly 

 lie flat on the curvature of the alveolus, proceed from the 

 nucleated central portion of the cell ; they do not however form 

 an interrupted investing membrane like basket-work to the 

 alveolus, but appear in the form of thickened striae and ribs 

 in a membrane firmly surrounding and enclosing the alveolus, 

 composed of these stellate cells in a manner of which it is not 

 very easy to give a clear description. The cells and their 

 processes, in their relation to the substance of the membrana 

 propria, may best be compared to the ribs of a leaf, or with 

 toes between which a swimming membrane is expanded. We 

 cannot however draw a completely sharp line of distinction 

 between the ribs and the substance of the membrane, or show 



* The only analysis of the tears of Man hitherto published, that by 

 Frerichs (in the article ' Tears,' in Wagner's Handworterbuch der Physio- 

 logic, Band iii., Abtheil i., p. 618), certainly admits the existence of a 

 small quantity of mucus. But in this instance the secretion of the 

 Meibomian follicles was not excluded. 



