PROTOTROPHIC BACTERIA 189 



water undesirable first for laundry purposes, and later for 

 drinking purposes, although the only objection here is an 

 aesthetic one. Their growth in the water pipes of a city 

 sometimes occurs to such an extent that the flow of water is 

 interfered with. Water calamities of this sort have been ex- 

 perienced by a number of cities, particularly Lille and Berlin. 



" There is reason to suppose that the masses of iron ore in 

 northern Minnesota upon the Mesaba range were deposited 

 there by the activity of iron bacteria living in the warm waters 

 of an ancient ocean. We may imagine such a primeval sea, 

 hot like the geysers of the Yellowstone, its waters impregnated 

 with iron and furnishing a splendid field for the peculiar ac- 

 tivities of the iron bacteria. Living in such an ocean for thou- 

 sands of years, as they have done, there is nothing unreasonable 

 in attributing to them the deposits of iron ore which during 

 these latter days are being mined for commercial purposes." 

 (Mac Mfflan.) 



Another representative of this group is Cladothrix odorif era, 

 which is commonly found in the soil and which gives the pecul- 

 iar odor to the soil such as that which is particularly noticed 

 after a rain storm. 



