234 ELIOT R. CLARK AND ELEANOR LINTON CLARK 
blood-vessels. In cases in which wandering cells were situated 
very near the point of injection, they stopped their amoeboid 
movement immediately after the injection and sent out fine 
processes. 
Several specimens were fixed in Bouin’s fluid and stained with 
Ehrlich’s haematoxylin and counterstained with eosin, orange G, 
and aurantia, and the whole tail mounted in balsam (fig. 13). 
These specimens showed leucocytes in stages of migration or in 
the stage in which they were covered with fine processes. In 
these specimens the polymorphonuclear leucocytes predomi- 
nated, but mononuclear cells, with an oval nucleus eccentrically 
placed, and a few cells resembling lymphocytes were also present. 
The behavior of all the non-pigmented leucocytes was the same 
regardless of the kind of nuclei they possessed. 
The reaction of leucocytes and wandering cells toward this 
injurious substance differs from their behavior toward the 
materials injected in former experiments. With sterile paraffin 
oil there was very little migration of leucocytes. Wandering 
cells of the tissue moved toward the globule, sometimes flattening 
out on its surface and then moving away again. The paraffin 
oil remained in the tissue without occasioning any disturbance, 
and after the first day or two no cells reacted toward it in any 
observable way. When carbon and carmine granules, previously 
sterilized, were injected into the fin, they were phagocytized by 
wandering cells which migrated toward them. In the case of 
injected fat (in the form of olive oil, oleic acid, cream, and yolk 
of egg) leucocytes migrated from the blood-vessels, going directly 
toward the injected substances and actively engulfing small 
globules of fat. In this case only part of the wandering cells 
were attracted toward the injected substances. 
Any explanation of the exact nature of the reaction of these 
leucocytes and wandering cells toward an injurious agent such 
as croton oil would be mere speculation. However, the obser- 
vations yielded abundant evidence that the formation of this 
barrier of stationary leucocytes with processes has a neutralizing 
effect on the oil and forms an efficient method of localizing the 
injury. It was noted in every case that connective-tissue cells, 
