Jan. IS, 1920 Further Studies of Sorosporella uvella 417 



PHAGOCYTOSIS 



During the course of these investigations a phenomenon was observed , 

 which, though well known in animal pathology, has received little or 

 no attention from insect pathologists. The discovery of this phenome- 

 non, phagocytosis, in cutworms infected with Sorosporella uvella may be 

 of considerable importance from the economic as well as the scientific 

 point of view; and while it is realized that the information given here- 

 with is far from complete, because the subject of phagocytosis and 

 especially its relation to immunity is not clearly understood, it is hoped 

 that the evidence submitted will show clearly that the vegetative bodies 

 of Sorosporella are ingested by the leucocytes of the infected hosts, a 

 condition that has generally been overlooked in previous investigations 

 of insect diseases. 



That such a condition has been overlooked is without doubt due to 

 the fact that the vegetative development of entomogenous fungi — that is, 

 those phases which occur within living insects — have never been studied 

 in much detail, although the external reproductive phases are in many 

 cases well known. 



When it was discovered that the fungus under consideration vegetates 

 within the blood of infected insects during the early stages of the develop- 

 ment, blood smears were made ; and after the usual preparatory methods 

 they were stained in Erlich's haematoxylin and eosin. In addition to 

 variable numbers of blastocysts, such slides always show large, spherical, 

 or spindle-shaped, free-floating cells which are of insect origin. Stained 

 preparations showing these cells were submitted to Dr. W. A. Riley, of 

 the University of Minnesota, who kindly informed the writer that he con- 

 sidered them typical blood corpuscles, or leucocytes. He recognized 

 four types, all of which are representative of the Lepidoptera: (i) Pro- 

 leucocytes, small cells, with large nuclei and little cytoplasm; (2) phago- 

 cytes, larger fusiform cells with central nuclei; (3) spherule cells, rounded, 

 vacuolate, and with irregular nuclei ; and (4) oenocytoids, large nonphago- 

 cytic cells with dense protoplasm. 



Of those four types only one, the fusiform cells, is of interest in the 

 present connection, since they alone seem to be phagocytic. These will 

 be considered below under the general terms leucocytes, or blood cor- 

 puscles, or the more specific term phagocytes. 



When blood smears of cutworms infected by Sorosporella are prepared 

 with the stains noted above, the vegetative budding cells of the fungus 

 are made clearly visible. Not only do they occur often in great abun- 

 dance, floating free within the blood plasm, but many may also be observed 

 firmly and distinctly imbedded within the cytoplasm of the leucocytes 

 (PI. 52, B-E), a condition that had escaped attention in water mounts, 

 in which there is of course no differentiation of contents of the leucocytes. 



