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MR P. BRUCE WHITE ON 
further, the procedure may occasion atrophic muscle changes which are only known 
to occur in that disease. When the first pair of spiracles is closed, a state of com- 
plete incapacitation results, ending rapidly in death. 
Though too close a parallel must not be drawn with the natural disease, these 
experiments are illuminating in that they give a basis to the view that the r61e of 
parasites in partially preventing thoracic respiration is of prime importance in the 
disease — possibly in itself capable of occasioning all the symptoms by which we are 
wont to diagnose the disease and the muscle atrophy so often associated with it. 
The pathological syndrome of Isle of Wight disease is undoubtedly complex. 
Apart from the sapping of the host fluids and the probable injection of a venom, 
the mites may impair the mechanism of the bee either by destroying the respiratory 
supply of the individual organs or by cutting off that of the nerve centres which 
control and co-ordinate their activities. It is possible that the indirect effect 
through the nervous system, possessed as this is of a dual respiratory supply, is 
particularly acute when there is considerable bilateral obstruction of the tracheal 
system. 
Through the combined influence of these factors the power of flight is lost, and 
a series of secondary conditions arise. 
The faeces normally voided on the wing accumulate, thus increasing the difficulty 
of locomotion and compressing the abdominal air-sacs — another blow at the respira- 
tory function. Intestinal pressure must hinder the excretory activities of the 
Malpighian tubules, and this excretory stasis, together with the absorption of toxins 
from the stagnant gut, must be reflected back upon the body of the insect. 
As soon as the power of flight is lost death of the bee becomes imminent, for 
once it leaves the warmth and stores of the hive, unable to return, it perishes of cold 
and starvation. Should it elect to remain within the hive it is faced with a prospect 
of functional stagnation which cannot be indefinitely maintained. It would seem too 
that in the colder months sick stocks often perish en masse through inability to 
maintain the hive temperature. 
It seems that in rare cases individual bees may recover from the attack upon 
being abandoned by the parasitic brood. Such cases are recognised by their bronzed 
and blackened tracheae, which, however, contain no living mites. Bees in this con- 
dition have been found foraging for infected stocks. 
Concluding Remarks. 
It is somewhat remarkable that the macroscopic changes of the thoracic tracheae 
and muscle have so long escaped observation in spite of the detailed examinations of 
several independent workers. 
Imms (l) held that “ the disease is eminently one of the digestive system, and 
might be described as a condition of enlargement of the hind intestine,” while 
