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XXIX. 
(2) The Pathology of Isle of Wight Disease in Hive Bees. By P. Bruce White, 
B.Sc., Bacteriologist to the Bee Disease Investigation, University of Aberdeen 
and N. of Scotland College of Agriculture. Communicated by Dr John 
Rennie. (With One Plate.) 
( From the Department of Pathology , Marischal College, Aberdeen.) 
(Bead November 1, 1920. MS. received December 7, 1920. Issued separately March 25, 1921.) 
Isle of Wight disease is, as we have seen, primarily a disease of the respiratory 
system, in which the organism remains localised throughout the entire course of 
the attack. 
The effects are, however, .far-reaching, and are registered in the disordered 
functioning of several organs, and in visible pathological changes in some of them. 
The parasitic invasion has two aspects. 
We have, in the first place, to consider the active injury wrought upon the host 
by a parasite developing and living at the expense of its body fluids. With this 
aspect of the question may be coupled the possibility of a definite toxic action on 
the part of the parasite. 
In the second place, we have to consider the passive. role of the mites in hindering 
or inhibiting the normal functions of the infected organs. 
Before proceeding to consider the various pathological conditions, a few words on 
the distribution of the parasite within the host is called for. 
In infected bees the mites are consistently present in the tracheal system of the 
thorax, and in a certain number of bees are also to be found in the air-vessels of the 
head. No mites have, up to the present, been discovered in the abdominal system. 
The primary parasitic invasion takes place through one or both of the first pair 
of spiracular orifices, and apparently through these alone. The whole anterior 
thoracic system of major tracheae and air-sacs is liable to infection. The infection 
may be unilateral or bilateral, and in some cases where the mites have entered on 
one side -only, they may migrate into the vessels of the other side, setting up 
a secondary bilateral infection. The passage is effected through the roots of the 
anterior air-sacs, which form a commissure between the large paired vessels 
supplying the head. 
A single mite may enter the bee, or several may enter together or at intervals. 
Sometimes the pregnant female may advance as far as the secondary tracheae before 
depositing eggs, but the primary trachea becomes involved sooner or later in the 
vast majority of cases. 
It is usually only in the later stages of the attack that the mites attain the 
smaller tracheae, the thoracic air-sacs, and the vessels of the head. In such cases, 
