ISLE OF WIGHT DISEASE TN HI YE 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 fibrillse, 
upon and between which lie the large flattened 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 different. 
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, 
