1 8 INFECTION AND IMMUNITY 



disease germs may find their way from the excreta 

 of the sick to the stomachs of healthy persons. If 

 thrown upon the ground, flies alighting upon the foul 

 material may subsequently visit a near-by kitchen 

 and there walk over the food prepared for the family 

 meal, leaving numerous typhoid bacilli in their tracks ; 

 or they may fall into the milk, or in some other un- 

 suspected way convey the deadly microscopic germs 

 to some article of food or drink. Again, articles of 

 clothing soiled by the discharges of the sick may be 

 the means of conveying infection to laundresses, who 

 in handling such articles are liable to soil their hands 

 or in some indirect way to introduce the pathogenic 

 bacteria into their mouths. This mode of infection 

 is liable to occur in any disease in which the germ is 

 present in the discharges from the bowels, and es- 

 pecially in Asiatic cholera. 



In Oriental countries, where human excreta con- 

 stitutes a very common fertilising material, green 

 vegetables, which are eaten raw, are believed to 

 serve as the medium through which the germs of 

 dysentery and cholera are occasionally conveyed 

 to the stomachs of persons partaking of such articles 

 of food. There is also considerable evidence in 

 favour of the view that typhoid fever may be con- 

 tracted by eating oysters which have been grown in 

 sewage-polluted waters. The infectious disease known 



