768 MODE OF SPREAD OF INFECTIVE DISEASES. 



Influence of 

 various 

 accidents on 

 the distribu- 

 tion of the 

 bacteria. 



It is often im- 



Sensible to 

 iscover the 

 caiise of the 

 local distribu' 

 tion of 

 epidemics. 



surrounding the wells, and that the observer has paid 

 but little attention to this defect, on the assumption that 

 in no other way could such a peculiar distribution of 

 the disease have occurred. 



To obtain an idea of the innumerable small accidents 

 which may influence the spread of the infective agents 

 in one or other direction, and that without the interven- 

 tion of drinking water, we only require to follow the fate 

 of a cultivation of some readily recognisable form of 

 bacterium, e.g., bacillus prodigiosus, when placed any- 

 where in a house. We can often observe how small 

 red colonies appear on various nutrient substrata and 

 articles of food, with regard to which it is evident, from 

 the place where they have developed or from the group- 

 ing of the colonies, that they have been carried by the 

 fingers, sleeves, table, or flies without intentional or even 

 conscious contact with the exposed cultivation. It 

 may further be observed that at one time the epidemic 

 is limited to the room in which the culture is ; at 

 another it suddenly appears in another and distant 

 room ; again it rapidly spreads over the whole house ; 

 or again it appears in neighbouring houses without any 

 affection of the immediate neighbourhood ; and lastly, 

 although the conditions are apparently the same, no 

 epidemic may occur. The result is so dependent in 

 each individual case on the most trivial accidents, that in 

 laboratories where much work is done with bacteria one 

 soon ceases to wonder at the peculiar and varying mode 

 of spread of this or that readily recognisable impurity. 



Exactly analogous are the sources of infection of 

 typhoid epidemics, whether originating from a patient 

 suffering from the disease, or from infected earth, or 

 from spores which have been carried to suitable nutrient 

 substrata, or from any materials which have been con- 

 taminated with typhoid dejecta. The mode, the direc- 

 tion, and the extent of the spread of the epidemic from 

 these sources depends on a great variety of accidents. 

 As in the case of the prodigiosus cultivation, the trans- 

 port by man and various objects will play a very 

 important rule ; the result in each case will, however, 



