no Jouryial of Agricultural Research voi. iv, No. 2 



The formation of the polyhedral bodies within the nuclei of the four 

 tissues above mentioned and the visible changes taking place within 

 these nuclei may be described as follows: The first indication of a dis- 

 eased nucleus seems to consist in the flowing together of the chromatin 

 into a lump in the middle (Pi. XTII, fig. 21). Then out of the achro- 

 matic substance the polyhedra arise as very minute individuals (PI. XIII, 

 fig. 22), which can be demonstrated to advantage by the hgematoxylin 

 method given under "Technique." By this method the polyhedra 

 are stained dark; by the use of Giemsa's stain they are merely faintly 

 outlined (PI. XIII, fig. 23). At this stage Giemsa's stain also clearly 

 shows many little granules in the nuclei (Pi. XIII, fig. 23) which are 

 identical with the dancing granules observed in fresh preparations. 

 They stain red and are either single or double, thus resembling tiny 

 micrococci. These granules may adhere to the periphery of the poly- 

 hedra or may lie above, below, or in the spaces between them. The 

 formative polyhedra themselves stain slightly along the periphery with 

 Giemsa's stain. As the polyhedra increase in size, they become more 

 and more refractive, do not stain at all finally, and the nucleus swells to 

 an enormous size (PI. XII, fig. 3; XIII, fig. 24). To obtain some 

 idea of the comparative sizes of normal and pathological nuclei in the 

 same tissue of the caterpillar, 12 normal and 12 pathological fat cell 

 nuclei were measured. The normal nuclei measured between 6 and i3^«, 

 the pathological nuclei from 7 to 29// in diameter. The early pathological 

 stages measured less than the later ones, and it is seen from the meas- 

 urements that the late stages of the hypertrophied nuclei are more than 

 twice as large as the largest normal nucleus. This swelling of the nucleus 

 is due to the increase in size of the polyhedral bodies, which stretch the 

 nuclear membrane. All the polyhedra seem to be in the same stage of 

 development within an individual nucleus — that is, great differences in 

 sizes between polyhedra within a single nucleus do not occur, but there 

 are, of course, enormous variations in sizes between those of separate 

 nuclei. The small polyhedra are somewhat rounder than larger indi- 

 viduals, which can be accounted for by the fact that, as the polyhedra 

 grow, they become so closely packed within a nucleus that they press 

 upon one another and thus the more or less polygonal shape is produced. 

 As the pol3^hedra grow and become more refractive, the little red gran- 

 ules stained by Giemsa's stain, as well as the remains of the chromatin 

 lump, disappear and there remains simply the nuclear membrane inclos- 

 ing the polyhedra (PI. XIII, fig. 24). Sometimes the chromatin lump 

 remains till the nucleus disintegrates, but most frequently it disappears 

 before this event. The nucleus swells more and more, finally the nuclear 

 membrane ruptures, and the polyhedra escape into the body cavity (PI. 

 XIII, fig. 25). Thus, the polyhedra are found free in great numbers in 

 smears of dead caterpillars. 



