REACTION OF CELLS TO CROTON OIL 249 
from connective-tissue cells: Minervini (711); e) leucocytes from 
endothelial cells: Cornil and Ranvier (’80) from lymphatic endo- 
thelium, Beattie (02), Evans (’14), from Kipffer cells in the 
liver, Marchand (713) and MacCallum (716), possibly in special 
organs, Mallory (14); f) leucocytes from connective tissue or 
reticulum: Herbert (01), Downey (712) in lymph glands. It 
is to be noted that the most of these studies have been made 
upon preserved material, in which deductions as to cell trans- 
formations are notoriously unreliable. 
In our investigation the cells were watched in the living animal, 
in a region in which it is possible to follow the changes of indi- 
vidual cells throughout the process of the tissue reaction to an 
injurious chemical agent. We were unable to find the slightest 
evidence for the transformation of a cell of one type into a cell 
of another type. Blood-vessel and lymphatic endothelial cells 
maintained their identity and did not give rise to wandering 
cells, nor was new endothelium formed by any other way than 
by the sprouting of preexisting endothelium. Leucocytes were 
not formed from connective tissue nor endothelium nor were 
they transformed into connective-tissue cells or endothelial cells. 
Connective-tissue cells maintained their identity completely 
throughout the entire process. This entire group of cells, then, 
remained specific, in an aseptic inflammation, in the transparent 
fin expansion of the tadpole’s tail, produced by the injection of 
croton oil. 
There were a number of appearances produced in the reaction 
of the various tissues which were so suggestive of possible trans- 
formations from one type to another that we were forced to 
make long continuous observations before arriving at definite 
conclusions. During the first season in which we studied this 
problem, we were nearly convinced that the leucocytes, after 
becoming sessile and sending out their processes, were actually 
transformed into connective-tissue cells. It was exactly this 
picture which led Metchnikoff to conclude that such a transfor- 
mation takes place. However, since we had been unable to 
follow the same cells through the entire period, we postponed 
publication of our results, until we might have another tadpole 
