224 ELIOT R. CLARK AND ELEANOR LINTON CLARK 
GENERAL PICTURE OF THE REACTION TO CROTON OIL 
Immediately after the injection of a small globule of croton 
oil, a decided change was noticeable in the fin near the site of 
injury. The whole region became more opaque than other por- 
tions of the tail. This opacity is due to a granular appearance of 
the epidermal cells and connective-tissue cells of the neighborhood. 
Higher magnification shows that their ‘granular’ appearance is 
caused by the formation of vacuoles in the cells. An opaque 
‘granular’ zone extends for a distance around the globule. This 
zone is wider proximally, toward the muscle, than it is in the 
region distally between the globule and the fin margin, evidently 
corresponding to the direction of flow of the currents of fluid in 
the tissue spaces. The processes of the connective-tissue cells 
in this zone are drawn in, the cell bodies become swollen and 
vacuolated, and the nuclei become visible. The endothelial 
cells of the lymphatic capillaries within this zone also become 
swollen and vacuolated and their nuclei show up plainly. 
Fifteen or twenty minutes after the injection a distortion of . 
the fin at the injured region may be observed. Most frequently 
this takes the form of a bend or fold in the fin. At other times, 
particularly with the stronger concentrations of croton oil, a 
blister forms around the Sieg which usually disappears 
within a few hours. ; 
In the main longitudinal re. eee of the tail and in the 
larger vessels situated near the muscle edge, the circulatory 
changes, described by early observers of inflammation, can be 
followed—the increased blood flow, followed after a half hour 
or more by a slowing of the current and a tendency of the 
leucocytes to stick to the vessel wall. In the capillary loops of 
the fin these changes are not so evident, owing to the narrowness 
of the vessels which permits the passage of only one corpuscle 
at a time. In such a capillary within the ‘granular area,’ the 
circulation usually ceases within an hour or two after the injection 
of croton oil. Wandering cells in the neighborhood are attracted 
toward the injected substance. 
