756 
MR P. BRUCE WHITE ON 
however, the young mites frequently advance as far as the .calibre of the vessels 
permits. 
The various pathological conditions which may be encountered in infected bees 
will now be considered, the various systems being treated of in sequence. 
Tracheal System. 
Macroscopical appearances . — The first change visible to the naked eye is an 
increased opacity of the infected vessels due to the aggregation of ova and the 
younger forms of the parasite within the lumina. As the disease advances the 
trachea assumes a brown tint, which gradually deepens and becomes flecked with 
black. Finally considerable portions of the infected tracheae may become dead black. 
This change in colour is accompanied by an increasing hardness and brittleness of 
the parts, which become rigid. This brittleness results in a phenomenon which is 
of some use in the field diagnosis of the disease. It is frequently found that upon 
exerting moderate pressure upon the upper surface of the thorax of bees crawling 
from the disease, that a drop of fluid — blood — will exude from the first spiracle of 
one or both sides, the rupture of the trachea at its insertion having thrown the 
hsemocoele open to the exterior. 
Microscopic appearances . — During the earlier stages of the attack, the oval and 
almost colourless ova and embryos may be seen lying within the lumina of the 
tracheae. The parent mites, too, may often be found in the vicinity. The tracheal 
wall may show here and there a few fragments of brownish matter, the faeces of the 
invading adults. 
This condition is maintained till, with the appearance of the later developmental 
stages of the parasite and the young adults, the wall becomes encrusted with granules 
of faecal matter. These granules, irregular in size and discoid or spherical in shape, 
become arranged in the interspaces between the tracheal thickenings, forming an 
irregular series of transverse bands upon the tracheal wall. They are of a brownish 
or yellowish colour, and when densely aggregated appear black. The colour of the 
deposit upon the wall therefore varies with the thickness of the crust and the 
amount of pigment it contains. The pigment may become extracted, leaving 
the pallid granules behind. 
A similar deposit may collect in the lacunas between the parasites themselves. 
A typically affected tracheal tube is shown in fig. 1, while a fragment of the 
encrusted wall is shown further enlarged in fig. 2. 
The faecal matter may, further, be inhaled and, though the bulk appears to be 
trapped in the air-sacs and larger vessels, may attain the finer ramifications of the 
system, sometimes forming small emboli in the tracheoles. This is particularly 
frequent when the parasites are present in the air-sacs. 
Careful study of the tracheal wall for perforations reveals little. In two cases 
