154 Tue MIcRoscopE. 
to add the glacial acetic acid undiluted to accomplish the de- 
sired result. The general effect is the same as that resulting 
from the use of the hematoxylin as recommneded above; in 
each case the staining fluid must be strong and the sections 
over-stained at first. 
The cartilage cells are quite difficult to preserve unaltered. 
A sper cent. solution of alum will preserve their natural 
appearance for some time. 
The cell districts may be shown by simple hematoxylin 
staining. The matrix will not take the staining uniformly, 
some parts showing a deeper color than others. 
Digesting the cartilage in water at 100° Fahrenheit will 
mark out the districts also; so will sulphuric and chromic 
acids, or a mixture of nitric acid and chlorate of potash. 
PIGMENT CELLS. 
Pigment cells are much more common in the lower than 
in the higher vertebrates. In the lower animals the connective 
tissue cells are filled with pigment granules of various colors 
from a jet black to a greenish or gray. Here the cells have 
long processes which anastomose with each other. The pro- 
cesses constitute about all of the cell, for only a nucleus is pres- 
ent where the body of the cell is usually 
found. These cells are capable of alter- 
ing their shape, for when subjected to 
certain irritants they can withdraw their 
pigment processes entirely, becoming 
changed into a round spherical body 
with a central nucleus. This change is 
under the control of the nervous sys- 
tem and accounts for the rapid chang- 
ing of color observed in many animals. 
It will be understood, however, that the 
ste colkg ey gonnective tis: Contraction of the pigment processes 
does not necessitate the contraction of the whole process of:the 
cell, for only a portion of the process of the cell is occupied by 
pigment. The cells may be spindle-shaped, or long and nar- 
row. They appear sometimes as large, flat plates, perforated 
with holes. The variety of shapes is largely due to the state 
of activity of the cell when undergoing examination. In the 
\ 
