ISLE OF WIGHT DISEASE IN HIVE BEES— PATHOLOGY. 757 



only has it been possible to observe the long piercing apparatus of the mite actually 

 passing through punctures in the wall. The material damage done in this way is 

 seemingly small. 



Muscular System. 



Visible pathological changes of the muscle fibres occur, but these are apparently 

 restricted to the thoracic muscles of flight. Though a considerable number of 

 fibres, in highly infected crawling bees, may show signs of the atrophic change 

 to be described, the number showing definite degenerative changes is usually small. 

 While no such changes have been noted in non-infected bees of whatever age, they 

 may occur in infected bees which show no outward symptoms of the malady. On 

 the other hand, a percentage of infected crawling bees show no marked muscle 

 changes. 



Macroscopic appearances. — Upon teasing out in saline the thoracic muscle mass 

 of a bee crawling from the disease it is usually found that certain fibres — averaging 

 2-6 in number — contrast markedly with the flaccid, greyish -yellow normal fibres by 

 their opaque white colour, slenderness, brittleness, and rigidity. 



Microscopic appearances. — Under the low power of the microscope these white 

 fibres are conspicuous by their slenderness, density, and granular appearance. The 

 ends show an irregular fracture quite unlike the frayed-out ends of the normal 

 fibres. A number of micrometer measurements on these and on healthy fibres of 

 the muscles of flight gave the following values : — 



Average width of healthy fibres of muscles of flight = "24 mm. 

 ,, ,, atrophied „ „ „ ='12 mm. 



In fresh preparations examined with the 1/6" objective it was possible to make 

 out the nature of the change which had taken place. 



In the normal muscle of the bee the bulk of the fibre is composed of the fibrillae, 

 upon and between which lie the large fiattened sarcosomes or myochondria. These 

 granules mask the transverse, but not the longitudinal, striation of the fibre. When 

 the fibre is teased out the fibrillse fray out, allowing the diaphanous sarcosomes 

 to escape. 



In the case of the atrophied fibres of infected bees the appearances are difiierent. 

 Microscopic examination may show little or nothing of the original fibrillar struc- 

 ture. It is often found that the bulk of the fibre is composed of densely arranged 

 longitudinal columns of closely packed and very coherent sarcosomes which do 

 not escape and float away when the fibre is teased out. Between these granular 

 columns it is found, upon closer examination, that remnants of the fibrillse persist, 

 though many may be reduced to thread-like vestiges of their original form. 



A drawing of the low-power appearances of normal and atrophied fibres is shown 

 in fig. 3, and a piece of atrophied fibre is drawn under the high power in fig. 4,, 



