18 



BULLETIN 431, U. S. DEPARTMENT OF AGEICULTUEE. 



Middle third. — WMle tlie color of the middle third is similar to 

 and often approaches in its shade that of the anterior, very frequently 

 it is considerably lighter. The ventral surface of this third (figs. 18 

 and 7) is less convex from side to side than in the preceding stage, 

 and the segmental markings, while still plainly visible, are less pro- 

 nounced. The notches along the lateral margins are also less pro- 

 nounced. 



Posterior third. — The color of the posterior third (figs. 18 and 7; 

 PL II, p) equals or exceeds in depth of shade that of the middle 

 third and sometimes equals that of the anterior third. The surface 

 markings are still pronounced and much resemble those of the 

 normal larva. 



That the watery content of the sac is being lessened through evapo- 

 ration is evidenced by the diminution of the quantity of the watery- 



FiG. 19. — Third stage: Larva dead of sacbrood, lateral view. (Original.) 



appearing substance seen at the lateral margins of the middle and 

 posterior thirds and by the wrinkling of the cuticular sac. These 

 wrinkles are small and numerous. 



The lateral view of the larva in the third stage (fig. 19) shows that it 

 stiU maintains, in a general way, the form and markings of the normal 

 larva (fig. 4). The turgidity is gone, although the position in the 

 cell is very much as it is in the healthy larva. 



Consistency of the sac and its contents. — It is the appearance of the 

 remains of the larva in the third stage of the decay that best character- 

 izes the disease, sacbrood. The cuticular sac is now quite tough, 

 permitting the removal of the larva from the cell with considerable 

 ease and with httle danger of its being torn. The content of the sac is 

 a granular mass, brownish in color and suspended in a comparatively 

 small quantity of a more or less clear watery-appearing fluid. Upon 

 microscopic exanunation the mass is found to consist of decaying 

 tissues, chiefly fat cells. 



Condition of the virus in the third stage. — When the larval remains 

 in this stage of decay are crushed and fed in sirup to healthy colonies 

 no sacbrood is produced, indicating that the dead larvae at this stage 



