1877.] The Study of Zodlogy in Germany. 401 
entery of a turtle. If the impregnation was not sufficient the 
lines do not appear, but that is also the case if it has been too 
prolonged, for then the cells fall off alto- 
gether. The membrane may be colored 
with hematoxiline or carmine, if so de- 
sired, after impregnation, and then the 
stained nuclei appear within the dark 
outlines making exceedingly pretty prep- pye. 74) MESENTERY OF ‘TOR: 
arations. TLE. SURFACE IMPREG- 
Maceration gives the means of isolating repose nea Speers 
layers of cells. If the skin of an amphibian, a toad, for example, 
be pinned out on a bit of cork and then placed in a dish of water 
containing three or four drops of strong carbolic acid to prevent 
the development of germs, and then left for a day or two, the 
superficial layer of cells may be peeled off with a pair of pincers, 
and so on, successive layers from day to day until the whole skin 
has been removed. The bits thus peeled off usually contain but 
a single layer of cells, and if colored with carmine they make very 
beautiful preparations. 
But besides investigating cells in their relation to one another, 
the histologist endeavors to determine the form of single cells, 
and employs therefor means of isolation or dissociation. These 
may be either mechanical, such as shaking up a tissue in a fluid 
or teasing it out with fine needles, etc., or chemical. Usually.a 
combination of the two is the most effectual. 
In most tissues the cells are united by intercellular matter, 
just as above described in the epithelium of the mesentery. 
This substance acts as a cement binding the cells together. In 
Some cases it reaches an extraordinary development, so that the 
cells come to be quite far apart, as in cartilage, for instance. 
But usually it is very thin, and may be dissolved, in some 
cases, without altering the appearance of the neighboring cells. 
The cells that line the intestine and stomach are particularly 
adapted to illustrate this action of certain chemicals. Thus if a 
Small bit of the wall of the digestive canal be left in alcohol of 
thirty per cent. for twenty-four hours, the lining cells all become 
loosened so that they are easily scraped off with a needle or scalpel, 
and if mounted in glycerine mixed with a little picrocarmine, | 
they become stained in a week or so, and show the details of © 
Structure of the single cells very admirably. 
Chromic acid has a similar action, and solutions of two parts in 
~ ten thousand of distilled water have a greac value from their so 
ene “~ RO, 7. 26 So 
