LACUNAR SYSTEM OF THE ALVEOLI. 460 



coloured ring. The alveoli themselves, uncoloured by the in- 

 jection, lie separately on a coloured ground, an appearance that 

 is often repeated with perfect regularity over a surface present- 

 ing forty to fifty alveoli. If the bloodvessels have been coin- 

 cidently injected with a different colour, as, for example, with 

 vermilion, their irregular peculiarly inconstant division and 

 red colour form a striking contrast to the very regular dispo- 

 sition of the system of canals injected with blue. In fine sec- 

 tions, the bloodvessels, running in the form either of straight 

 or tortuous red lines, or, when seen in section, of red points 

 only, are invariably surrounded by a blue-coloured space, 

 identical in fact with that which surrounds each individual 

 alveolus. These appearances, repeated with unvarying regu- 

 larity in every section, admit of no other explanation than that 

 an extraordinarily rich, freely intercommunicating system of 

 fissures traverses the parenchyma of the entire gland, surround- 

 ing every alveolus and every bloodvessel. It is not that there 

 is a separate sheath for each alveolus and bloodvessel, consti- 

 tuting a peri-alveolar or perivascular space, but a single, con- 

 'inuous, very complicated cavity surrounding every parenchy- 

 matous body, which completely separates the bloodvessels from 

 the alveoli, and which everything that the blood brings to the 

 secreting parenchyma must first traverse before it can enter 

 into the secretion. 



The already extremely complicated hlstological and topo- 

 graphical relations of this cavity are rendered still more com- 

 plicated by the circumstance that a very rich system of various- 

 sized fibres, as well as of stellate cells, is stretched in its interior 

 between the alveoli. On sections of the hardened gland these 

 cells and their processes may be very easily demonstrated. 

 They are to some extent in relation- with the stellate cells com- 

 posing the membrana propria, whilst a few processes also run 

 out to adjoining alveoli, fastening and attaching the walls more 

 or less intimately together. Not unfrequently also cells are 

 found which, lying between two alveoli, belong as much to the 

 investing membrane of the one as the other, sending their pro- 

 cesses into both. Cells are also frequently found lying almost 

 perfectly free between the alveoli, or connected only very loosely 

 by means of their processes. It is remarkable that these inter- 



