280 Illinois State Laboratory of Natural History. 



were not different from those observed in cases of undoubted 

 flacherie, but they were usually far less numerous, a fact which 

 has suggested to me the following theoretical explanation of 

 the supposed jaundice of the silkworms at the University. 

 Assuming that the mortality was originally caused by the 

 intestinal bacteria, we may suppose that this infection was not 

 sufficiently overwhelming to destroy life by direct action, as 

 seems to be the case in flacherie, but that it nevertheless had 

 the effect to so disturb the balance of physiological functions 

 as to retard the development and preparation for pupation of 

 some of the organs, while the fatty bodies, being special stores of 

 material accumulated for use in pupation, and so less promptly 

 and easily affected by causes attacking the general health of 

 the larva, went on to pupation and experienced the histolysis 

 characteristic of that phenomenon. In other words, we may 

 suppose, quite consistently with all the facts, that a relatively 

 slight bacterial attack took uneven effect on the various parts 

 of the animal and not immediately destructive effect on any ; 

 that it retarded the preparations for pupation of the great 

 vital organs, but that the fatty bodies, as if unaware of this 

 fact, continued their course of maturation and histolysis, reach- 

 ing a condition of pupal disorganization before pupation had 

 actually occurred. 



The condition of the fatty bodies of the larva affected by 

 the supposed jaundice is well illustrated by slide 4732 of our 

 collections, containing portions of the fatty bodies of larvse 

 received from Prof. Burrill on the 30th July. The cells of 

 these organs, when examined under a power of 500 diameters, 

 were found, nearly all of them, to have undergone a remarkable 

 change. The contents of a few still remained minutely granu- 

 lar, a large nucleus being also occasionally visible, but the con- 



or in the silk tubes. These micrococci are very distinctly visible, shin- 

 ing with a reddish light when slightly out of focus, not being rendered 

 transparent by the mounting medium as are the tissues of the larva. 

 They are arranged in patches and strings, the former of irregular shape, 

 the latter sometimes containing as many as eight or ten spherules. The 

 fatty bodies of this larva are almost solid masses of mulberry granules. 

 The Malpighian tubules of another specimen show also, besides their 

 normal crystalline contents, great numbers of these mulberry granules, 

 formed within the cells or derived from outside sources. 



