24 BULLETIN 431, TJ. S. DEPARTMENT OP AGEICULTURE. 



The molt skin (Cj) is probably the one that is shed nonnally. about 

 three days after the larva is capped. The cuticula (Ci), already quite 

 well formed, is probably the one which normally would have entered 

 into the formation of the molt skin that is cast at the time the larva 

 or semipupa changes to a pupa. The molt skin (Cj) constitutes for 

 the most part the sac which is seen to inclose the decaying larval 

 mass in sacbrood, the cuticula (Ci) probably assisting somewhat 

 at times. The presence of the subcuticular fluid is made more intelli- 

 gible by these facts. Larvae dying of sacbrood at an earlier or later 

 period in their development will present an appearance varying 

 somewhat from that just described. 



Contrasted with the stomach (midintestine or midgut) of a feeding 

 larva, the stomach (A, St) of a larva at the age at which it dies of sac- 

 brood is small. The cells lining the wall of the organ vary con- 

 siderably in size and shape, depending upon the exact time at which 

 death takes place. In contrast to the low cells of the stomach wall in 

 younger larvse, the cells (E, SEpth) at this later period are much elon- 

 gated. These cells would also at times be found in the decaying 

 granular mass present in the larval remains. 



The various organs of the body contribute to the cellular content 

 of the decaying larval mass. At the period at which the larva dies 

 of sacbrood, the cellular changes accompanying metamorphosis are 

 particularly marked. This condition introduces various cellular ele- 

 ments into the decaying larval mass. 



The granular mass from the larval remains in sacbrood is, therefore, 

 a composite affair. Upon examining the mass microscopically, it wiU 

 be found that the granular appearance is due for the most part to 

 fat cells suspended in a liquid. The Mquid portion seems to be 

 chiefly blood of the larva, or, at least, derived from the blood, although 

 augmented most probably by other liquids of the larva and possibly by 

 a hquefaction of some of the tissues present. The granular mass 

 suspended in a watery fluid, as a symptom of sacbrood, is by these 

 facts rendered more easily understood. 



CAUSE OF SACBROOD. 



DooUttle (1881), Jones (1883), Simmms (1887), Root (1892 and 

 1896), Cook (1902), Dadant (1906), and others through their writ- 

 ings have pointed out the fact that there are losses sustained from 

 sacbrood. There has been no consensus of opinion, however, as to 

 the infectiousness of the disease. On this point Dadant (1906) 

 writes: 



Wliatever may be the cause of this disease (so-called Pickled Brood), and although 

 it is to a certain extent contagious, it often passes off without treatment. But, as 

 colonies may be entirely ruined by it, it ought not to be neglected. 



