REACTION OF CELLS TO CROTON OIL Zap: 
inate, while mononuclears are much more numerous later. This 
is explained by many as due to the destruction of polymorpho- 
nuclears. In our study we saw very little, if any, destruction of 
leucocytes. Moreover, the rounding up of all non-pigmented 
leucocytes after the extrusion of croton oil and retention of this 
shape for several days has led us to wonder whether in this 
phase the nuclei also round up. This point we hope to take up 
in future studies. 
SUMMARY 
The reactions and changes undergone by the cells in the tail 
of Amphibian larvae in response to injections of minute globules 
of croton oil are as follows: 
1. Connective-tissue cells manifest all grades of injury, 
depending upon their nearness to the oil. In the nearest cells the 
branched processes are withdrawn, the body of the cell becomes 
much swollen and vacuolated, and the nucleus becomes easily 
visible. Later, the vacuoles run together and the cell becomes a 
delicately walled sac, containing a few granules suspended in 
fluid. Later, the outlines of the cell are lost completely. Com- 
plete destruction, however, is limited to a very few cells. A 
little further away, cells become swollen and vacuolated, processes 
become much shorter, but are not retracted entirely, and the 
nucleus becomes visible, and may be indented by vacuoles. 
Such cells may recover completely—the vacuoles disappear, the 
cell becomes smaller, the nucleus less distinct, new processes are 
sent out and movement of the cell resumed. Still further away, 
the cells may show merely slight swelling with granulation. 
The cells on the border zone of the area affected react by moving 
toward the oil—at a rate much faster than the normal rate of 
movement of these cells. In this movement, the number and 
length of their processes are much reduced, until they resemble 
the typical filoblast. 
2. a) Non-pigmented leucocytes (including the wandering cells 
outside the blood-vessels) respond immediately by moving toward 
the globule of croton oil. When about half-way between the 
outer limits of the affected connective-tissue cells and the oil, 
