Studies on lymphocystis tumor cells of fish; the osmiophilic granules of the cytoplasmic inclusions and their interpretation as elementary bodies of the lymphocystis virus.

Summary and Conclusion The lymphocystis virus disease of fish is characterized by the enormous growth of the infected fibroblasts which are transformed into the so-called lymphocystis cells. In the cytoplasmic inclusion bodies of the lymphocystis cells of flounders and perches, granules have been demonstrated which give an intensive osmium reaction when exposed to osmic acid solution for several days. The number of these osmiophilic granules increases considerably during the growth period of the inclusion bodies. It remains an open question whether this increase in number is the result of divisions of the granules or the result of a progressive differentiation of the granules in the basophilic inclusion substance. After the break-down of the basophilic framework of the inclusions at advanced stages, clusters of the granules become scattered through the cytoplasm of the host cell. Most of the osmiophilic granules are small corpuscles of a rather uniform size of about 0.375 microns in paraffin sections. In addition to this small type some larger forms have been observed. The granules studied in fresh preparations are rather strongly refractive. They are resistant to a weak acetic acid solution. As far as can be judged on the basis of a solely morphological study with the light microscope, the osmiophilic granules of the lymphocystis inclusion bodies apparently correspond very well to the elementary bodies of other macroviruses. They are interpreted as the transmission stages of the lymphocystis virus.