240 ELIOT R. CLARK AND ELEANOR LINTON CLARK 
The vacuolization of the last two types has been described 
recently by Lewis (719) in studies of the ‘degeneration granules 
and vacuoles” of cells in tissue cultures. In our studies it is 
noteworthy that cells showing such marked ‘degenerative’ 
changes could recover so rapidly and completely. As soon as 
the ring of sessile leucocytes had formed, the vacuolated con- 
nective-tissue cells, outside of this barrier, became clear and 
refractile, the cell bodies became slender and were occupied 
solely by the nucleus, and the long branching processes again 
extended to their normal length. After the extrusion of the 
croton oil, practically all of the connective-tissue cells returned 
to normal and their recovery was amazingly rapid. Only one 
or two cells were lost and these were always cells which had 
previously shown the most extreme type of injury. One of 
these cells, watched continuously, became paler and paler and 
finally remained as an outer rim with a few granules inside 
before disappearing entirely (fig. 10, D). On the other hand, a 
number of cells which had shown the most extreme type of 
reaction toward the irritant were followed throughout the in- 
flammation and were seen to recover completely soon after the 
extrusion of the oil (fig. 9). 
This vacuolization and rounding up of the connective-tissue 
cells, in contrast to the behavior of the leucocytes, is a purely 
passive reaction. However, in the later stages of the process, 
after the extrusion of the croton oil, these cells play a very active 
part. They wander actively toward the gap in the tissue left 
by the extrusion of the oil, and some of them disappear from 
view temporarily, in the opaque regions at the site of the injury. 
During this period of migration, the processes of the connective- 
tissue cells radiate towards the injured region. The ends toward 
the gap are brush-like in appearance, while the opposite ends 
are rounded (fig. 11). One of the authors (E. R. Clark, 712) 
had previously studied the connective-tisssue cells in the normal 
tadpole, and found, by observing the same cells for several 
weeks, that they are not fixed, but constantly change their 
position, in most cases gradually wandering in the direction of 
the fin margin. However, after the extrusion of the oil the con- 
