Mayis, I9IS Wilt of Gipsy-Moth Caterpillars 109 



PATHOLOGY OF THE TISSUES 



As stated previously, owing to the fact that dead caterpillars disinte- 

 grate completely, they can not be used for sectioning; so one has to rely 

 entirely on living, diseased material. By sectioning large numbers of cater- 

 pillars or by infecting a number of individuals and sectioning one every 

 few days, all stages of the disease can be obtained. The writer has sec- 

 tioned between 600 and 700 individuals in all stages of development, 

 from the fully formed embryo within the egg up to the pupa. Polyhedral 

 bodies have never been found in gipsy-moth eggs, although both appar- 

 ently normal eggs and eggs that did not hatch were carefully examined. 

 The pathological conditions in the post-embryonic stages — i. e., from the 

 first to the sixth or seventh instars — were found to be exactly alike, 

 showing that the pathology does not vary at different ages. 



If the anterior and posterior ends of an infected caterpillar be cut oflf 

 so that the alimentary canal can be pulled out easily, one will find on 

 examination under a low-power microscope that the trachea and its 

 finer branches have grapelike clusters of rounded bodies attached to them. 

 Upon examination under the high-power dry or oil-immersion lens, 

 however, one finds that the clusters are simply masses of polyhedral 

 bodies within the nuclei of the tracheal matrix cells. (PI. XII, fig. 2.) 

 The nuclei of these cells seem to be among the first to be affected, for 

 often one will have no difficulty in finding polyhedral bodies around the 

 tracheae, when none will be revealed by a careful search in the other 

 tissues. Later, the polyhedral bodies appear also within the nuclei of 

 the hypodermal, fat, and blood cells. If the pathological nuclei in their 

 earlier stages — i. e., before the polyhedral bodies have reached their final 

 stage of development — are carefully examined under oil, many minute 

 violently dancing granules will be found within them. The dancing 

 granules may be particles of degenerated chromatic or achromatic sub- 

 stance, but the activities are so violent even in a preparation from which 

 all air currents have been excluded with vaseline that the writer is 

 inclined to think that there was more than molecular motion and that he 

 was confronted with the behavior of extremely minute micro-organisms. 

 These granules are similar to those found in the fresh smears of dead 

 caterpillars mentioned previously, in distinguishing between pigment 

 and other more violently dancing particles. For reference to these 

 bodies in stained sections, see page 1 10. 



Stained sections show that the polyhedra originate within the nuclei 

 of the hypodermal, fat, tracheal matrix, and blood cells. The writer has 

 been utteriy unable to find polyhedra within the nuclei of the muscles, 

 Malpighian tubes, ganglia, or nerves. It is also interesting to note that 

 polyhedral bodies have never been found within the nuclei of gland cells, 

 such as setiferous cells, intestinal epithelial cells, cenocytes, salivary 

 glands, and gonads. 



