21,¢  Mendoza-Guazon: Schistosomiasis in the Philippines 589 
scesses thus formed, the ova are discharged into the lumen of 
the intestinal canal or into the peritoneal cavity. 
Lanning,(18) from an examination of pathological slides, 
thinks that a mass of ova collects in the lymphatics of the 
intestinal submucosa, which causes pressure necrosis of the 
surrounding tissue, and so the mass of eggs is extruded into 
the bowel lumen. This accounts for the fact that ova are very 
often not found in the stools for a long period of time and, 
again, will be discovered in a small quantity of blood and mucus 
in large numbers. 
REACTION OF THE DEFINITIVE HOST 
Local necrosis is produced either by the toxic substance 
secreted by the contained miracidium in the ovum or by the 
pressure of the ovum or ova. The toxin plus the necrotic sub- 
stances probably exert a chemotactic influence on the endothe- 
lium leucocytes, on the eosinophile leucocytes, plasma ‘cells, 
lymphocytes, and fibroblasts. An isolated ovum is usually en- 
circled by foreign-body giant cells, and in many instances one 
cannot but believe that these giant cells are formed by the 
coalescence of endothelial leucocytes. Sometimes the ovum is 
- completely dissolved by these cells, as demonstrated by the 
pieces of transparent shell in their cytoplasm (Plate 38, fig. 1). 
In case the injury is severe and one or two foreign-body giant 
cells are not sufficient to counteract the injurious agents, then 
the lesion produced, as well as the tissue reaction, is similar 
to the infective granulomata. In the periphery of the eosin- 
stained necrotic center are epithelioid cells, giant cells, fibro- 
blasts, and eosinophile leucocytes. They are inwrapped by 
circularly arranged fibroblasts and eosinophiles which merge 
into the outermost zone of fibrous tissue, eosinophiles, and small 
lymphocytes. : 
Should the nodule be located near a mucous surface, secondary 
pyogenic infection may take place and the nodule may either 
ulcerate or perforate, as in autopsy 4676, where a generalized 
suppurative peritonitis was apparently caused by the presence 
of masses of ova in all the coats of the appendix. In many 
instances an ovum or a mass of ova becomes encapsulated by 
fibrous tissue and eosinophiles and undergoes calcification. In 
the long run the outcome of this type of lesion is marked 
fibrosis. 
Fairly,(12) in his investigation of immunity reactions in 
Egyptian bilharziasis, found that the cellular reaction is charac- 
