760 
MR P. BRUCE WHITE ON 
mass, and the few sections which have been examined of the anterior thoracic ganglia 
of sick and healthy bees show no alterations which cannot be accounted for as 
physiological variations due to senility. 
Discussion. 
With these facts before us an attempt may be made to discuss the correlation 
between the action of the parasite, the pathological changes, and the symptomatology 
of the disease. 
We have alluded to the two aspects of the primary effect of the parasite upon the 
host : the active injury produced by a parasite living upon the host fluids, with the 
added probability of a toxic action, and the passive obstruction of the- respiratory 
system of the head and anterior thorax. 
The pregnant parasites producing many, relatively large ova, the developing 
brood and the young adults must make considerable demands upon the host. It has 
been pointed out that the blood of crawling bees is often scanty, but it is improbable 
that this is in any significant degree directly due to the mites, but arises from the 
fact that fluid lost by excretion and transpiration is not replaced owing to the 
inability of the stricken bee to take or to obtain food. As many heavily infected 
bees continue to forage, though their tracheae are bronzed and blackened by long 
sojourn of the mites, it would seem probable that nutritive sapping does not per se 
render the bee effete. 
The same uncertainty surrounds the question of a toxic action. One member at 
least ( T . intectus) of the genus to which the parasite belongs is known to be 
venomous, but the exact importance of this factor in the disease must, like the 
foregoing, remain for the present a matter of surmise. 
The passive action of the parasites and their products in partially or completely 
blocking the infected tracheae is a factor of which the importance is much more 
readily estimated. 
It is obvious that any obstruction of the tracheal lumen must reduce the 
efficiency of the respiratory exchange of the organs supplied. In the vast majority 
of crawling bees the effective lumina of certain of the major tracheae are obviously 
very much reduced, and in some all but obliterated. The organs supplied by such 
tracheae must be reduced to an acute degree of oxygen starvation, and among the 
organs of which the respiratory supply is thus endangered are those of the head and 
the thoracic muscles of flight. 
It is clear that the effects must vary from case to case : — 
(a) With the degree of the obstruction. 
( b ) With the position of the . obstruction. 
(c) According as to whether the obstruction is bilateral or unilateral. 
The actual number of parasites distributed through the respiratory system is from 
