446 • 



occurs in his includinpf grasserie among tLe four typical diseases of 

 silk- worms,* and the remark made later on the same page: " Once only 

 have I seen the grasserie destroy a brood." Still it must be remembered 

 that Pasteur knew nothing of silk-worms prior to his studies on the 

 pebrine, and that his observations of silk-raising generally had not been 

 extensive. The disease is known to our silk-raisers under the name 

 of jaundice, but except as applied to the yellow races this is a mis- 

 nomer, as the white and green varieties turn milky, not yellow, when 

 attacked with the malady. It is to the yellow races that I shall here- 

 after refer unless otherwise stated. 



'f The disease makes its appearance when the worms are about to molt 

 and is most severe when it occurs during the fifth age, just at the spin- 

 ning time. The first signs of the trouble are small pale yellow spots 

 which appear around the stigmata. These spots gradually expand, 

 others appearing on the elevated portions of the rings, until they cover 

 the whole body ; at the same time their yellow color becomes deeper. 

 Simultaneously with this discoloration, the anterior rings (often mis- 

 taken on account of their shape for the head of the larvae by persons 

 unacquainted with its anatomy) begin to swell, this being soon followed 

 by the distension of the other rings to such an extent that the interan- 

 Bular spaces appear like strangulations. The stretched skin becomes 

 bright and tender, and finally, unable longer to resist the strain, it 

 bursts, at first at the joints of the rings and later in other places, per- 

 mitting the discharge of a troubled dirty liquid which soils the food 

 of neighboring worms. The body afterwards putrefies and turns black, 

 more slowly than in flaccidity and all over at once, not beginning near 

 the anterior pair of prolegs, as is the case with the latter disorder."! 



When the worm is cut open in the early stages of the disease, that is to say, when 

 the first little yellow spots are discovered about the stigmata, no changes in the 

 internal organs can be seen with the naked eyes, only the blood appears turbid and 

 railky. Henceforth the worm refuses food and crawls about uneasily. In 12 hours 

 or even in less time its whole bodj^ has become yellow, and the feeble skin allows the 

 now quite opaque blood to ooze out. The stomach is sometimes full of leaves of a 

 bluish green color, and sometimes contains a more or less transparent liquid, which 

 either wholly or partially fills its cavity. In the latter case vomiting often occurs. 

 In the caecum or the rectum, or m both, a large brownish mass is found, which is 

 formed of minute particles of leaf. 



When the disease is far advanced a careful observer will often find on the peritracheal 

 membranes of the larger tracheje, on the epithelium of the silk-bearing glands, on 

 the muscles, and even on the nerves, whitish spots which interrupt the transparency 

 of the organ, and which in appearance are similar to the whitish spots of the silk- 

 bearing glands of highly corpusculous worms. * " * 



If at the beginning of the disease the blood of the worm is examined with a micro- 

 scope, it is found that the turbidness is caused by very minute polyliedral granules 

 floating in the plasma or inclosed in the blood globules (Fig. 1, a). These granules 

 are also constantly found in the cells of the adipose tissue, where they gradually in- 

 crease in number as the disease progresses, until the cells are filled with them to 



* Etudes sur la Maladie des Vers a sole, vol. i, p. 225. 



t "The Mulberry Silk Worm," Bulletin 9, Division of Entomology, plate i, fig. E., 



