REACTION OF CELLS TO CROTON OIL 243 
this ‘granular area’ was always observed. On the contrary, the 
vessels just outside this zone usually showed a tendency to send 
out new sprouts during this period. A day or two after the 
extrusion of the globule during the stage of repair, the vessels of 
the injured area began to send.out new sprouts and formed new 
loops once more. 
The reaction of the blood-vessel endothelium toward the 
croton oil appeared to be entirely passive. Ina number of larvae 
records were kept of the nuclei of the blood-vessels both inside 
and outside the injured area, but no unusual changes were noted. 
There was no sign of any proliferation of endothelial nuclei to form 
wandering cells or endothelial leucocytes. Occasionally leuco- 
cytes were observed to flatten out on the interior of the wall of a 
blood capillary and to pass through the wall sideways. During 
this process there were moments at which such a leucocyte 
greatly resembled a nucleus protruding into the lumen of the 
vessel, and a little later it appeared very much like a nucleus 
detaching itself from the wall. However, in the consecutive 
observations of living specimens it was always possible to follow 
the individual endothelial nuclei and to observe that the phenom- 
enon consisted of the emigration of a leucocyte through the wall, 
rather than the formation of a leucocyte from an endothelial 
cell. 
THE LYMPHATICS 
The lymphatic endothelium plays both an active and a passive 
part in the inflammation set up by the presence of a drop of 
croton oil. The lymph capillaries within the ‘granular area’ 
show the changes characteristic of injury displayed by the 
connective tissue and epithelial cells. The areas surrounding 
the nuclei of the lymphatic became swollen, opaque, and vacu- 
olated, particularly toward the tip. Such vessels usually 
retracted at about the time of the extrusion of the oil. A day 
or two later they sent out new sprouts into the regeneration area. 
The vessels outside the ‘granular area’ showed the fine processes 
characteristic of functional activity (E. R. Clark, ’09) and even 
continued to increase in length during the period of active inflam- 
