( 48 ) 
The coloring of the cartilage was attempted with full-grown objects, 
as well as with embryos, but as the coloring-method is chiefly useful 
when applied to small objects, with which the ordinary preparation- 
method proves deficient, it will chiefly be applied to embryos. 
Whenever we wanted to examine the cartilaginous skeleton of an 
embryo, we were, up to the present time, obliged to make series of 
sections and to construct an enlarged model after these sections, all 
of which took up a good deal of time. As arule it would have taken 
much too long to model a whole skeleton ; therefore in most cases 
only a part was constructed, for instance the head-skeleton or 
the pelvis. 
Working on this plan a single object requires many months of 
labor, and besides at the end you have not the object itself, but an 
imitation. 
Following the coloring-method, on the contrary, a great number 
of entire skeletons are obtained in a short time with little trouble, 
not clumsy imitations, but the objects themselves with all parts in 
their natural connection and the contours of the whole embryo and 
of different organs besides, for notwithstanding the transparency of 
the organs the outlines of many are still clearly recognizable. Although 
the cartilage is colored intensely blue, it remains transparent: so 
for instance the spinal column glimmers through the shoulder-blade. 
The method is as follows: 
The embryo is fixed in the usual way in 5°/, sublimate-solution, 
or 10°/, formol, or in ZeENKER’S liquid and is preserved in alcohol. 
No doubt it may be fixed in many other ways; I even obtained 
useful results with old preparations of alcohol from the collection. 
I mostly fix the embryos in 5°/, sublimate-solution, to which is added 
‘/,, Volumen formol, shortly before using. 
The object may now be brought immediately from the alcohol 
into the pigment-solution, but it has seemed advisable to me to extract 
previously for a day or two with alcohol, which contains some 
(*/,°/,) hydro-chlorie acid. The acid aleohol must be renewed if it 
has turned vellow the next day, which often happens when iodine has 
been used in extracting the sublimate. The iodine is fatal for the 
coloring, as it forms with methylene-blue an almost insoluble preci- 
pitate and with neutral alcohol the iodine cannot be quite removed. 
This is proved when seemingly white objects, preserved for a year 
and more in aleohol which has remained colorless, being brought 
into acid alcohol, cause this liquid to turn yellow the next day. The 
yellow color disappears after the addition of a few drops of sublimate- 
solution, 
