Bivalves in Relation to Disease 167 



feared on account of its insidious and dangerous nature, 

 is without doubt sometimes communicated to man by 

 oysters, and certainly may frequently be so transmitted 

 both by this form and by other shell-fish that are eaten 

 uncooked. 



Typhoid fever, known and dreaded nearly everywhere, 

 is caused by a rod-like bacterium or bacillus that enters 

 the body through the digestive tract. Several sources of 

 infection are very well understood. The most common 

 is drinking water, and many epidemics of the disease 

 have been traced to it in ways that do not admit of doubt. 

 Milk, also, is often the medium by which it is introduced, 

 but here the real sources have been proved to be the per- 

 son handling the receptacles for it or, more often, the 

 water in which cans or bottles have been washed. The 

 recent epidemics of army camps also have shown that the 

 organisms may be introduced into the digestive tract on 

 solid food. In such cases flies that have gathered in- 

 fected material on their appendages alight on food ready 

 to be eaten, and leave some of it there. It is probable 

 that the bacillus of typhoid passes through the digestive 

 tract of the fly without being injured, and if allowed to 

 do so, the fly deposits its digestive tract discharges on 

 food. Within a considerable distance of a typhoid fever 

 patient — or convalescent for that matter — these 

 creatures, formerly regarded merely as pests, become 

 deadly enemies. It may also be stated as a fact that 

 epidemics are sometimes caused by eating uncooked 

 oysters. Several times they have been traced directly 

 to that source. The evidence collected on that point in 

 this country and abroad is conclusive, and a biological 

 study of the habits of this and other bivalves clearly in- 

 dicates the way in which the transmission is accomplished. 



