198 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. 



AVith 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 eff"ete. 



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. 



(6) 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 



