194 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 treatedof 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 

 haemocoele 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 lacunae between the parasites themselves. 

 A typically aff'ected 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 



