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F. S. BILLINGS. 
condensations, we find round or oval nucleii from 0.003-0.006 m.m. in 
size surrounded by a thin layer of protoplasm. For the histological 
unity of the homogeneous membrane with its striae-like thickenings, 
speaks not only the transformation of this condensation in the mem¬ 
brane, but also the circumstance that this membrane could not be iso¬ 
lated by penciling nor through shaking it in distilled water. The mem¬ 
brane was uncolored by arg. nit. (half p. c.), whilst the glandular epithe¬ 
lium was stained yellow or brownish yellow ; the membrana propria 
offered a tolerably obstinate resistance to the action of weak acids and 
dilute alkalic solutions. I found the membrana propria of the mam¬ 
mary gland ot the cow had the same proprieties as other acinous glands 
as described by Boll (Bietrage zur mikroskopischen Anatomie der Acin- 
osen Driisen. Berlin, 1869). The interalveolar connective tissue is of 
a fine, fibrous variety containing oval and spindle-formed cells, which 
are often united to the membrana propria by their processes. The 
diameter of the interalveolar connective tissue is, as a rule, from 0.003- 
0.006 m.m. Between the blood capillaries of the interalveolar connec¬ 
tive tissue and the outer surface of the membrana propria, we find en¬ 
circling the alveoloe as described by Coyne (Centralblatt f. d. med. Wis- 
sench, 1815, p. 110), in the mamma of the human subject. In order 
to convince myself of the existence of perialveolce (periacinic) lymph- 
spaces, I injected into the interalveolar connective tissue of the mam- 
mary gland of a fresh slaughtered cow a half per cent, solution of arg. 
nit. In several preparations we observed black or brown rings around 
the alveole which I am inclined to consider as lymph-spaces filled with 
arg. nit. In other specimens I detected these rings in connection with 
lymph-capillaries. 
The lacteal ducts are lined with a single layer of cylindrical epith¬ 
elium from 0.015-0.018 m.m. in length, and 0.006-0.012 m.m. in diam¬ 
eter. These cells possess a fine, granular protoplasm with an oval nu¬ 
cleus 0.003-0.006 m.m. in diameter which is situated near the mem¬ 
brana propria. The contours of the protoplasm cannot be distinctly 
distinguished in fresh preparations, so that it is difficult to distinctly 
define single cells. 
1 he nucleus in fresh preparations is refracting, but those treated with 
Muller’s fluid and alcohol become granular. Between the basic ends of the 
cylindrical epithelial cells one sees, here and there, small, round, oval 
cells, containing large granules, from 0.003-0.006 m.m. in diameter, the 
so-called subepithelial cells (germ cells). The cylindrical epithelial cells 
are not so projecting in the small, excretory ducts as they are in the 
