1864.] CHEMISTRY OF MANURES. 109 



only prepared tlie way for it, but have, at the same time, rendered 

 its advent an indispensable necessity ; as a very brief consideration 

 will show. 



It is, in the first place, by the operation of steam-power that the 

 handicrafts, formerly pursued by families dispersed in villages over 

 the whole surface of the land, have been replaced by manufactures, 

 conducted in colossal factories, determining the agglomeration of 

 enormous populations, in rapidly developed towns and cities, 

 located usually (for the convenience of trade) upon streams and 

 rivers leading to the sea. 



Food has naturally followed population ; and corn and cattle, 

 vegetables and fruit, are daily poured from the country into the 

 towns, in streams of constantly increasing magnitude. The quan- 

 tity of fertilizing residua resulting from the consumption of these 

 provisions, and requiring, in fair husbandry, restoration to the 

 distant fields from which they come, undergoes, of course, propor- 

 tionate augmentation ; and the problem of their re-conveyance to 

 the land has been, and still is, one of annually increasing diffi- 

 culty. 



During the earlier development of the factory-system, the old 

 mode of urban defecation, by means of cesspools emptied periodi- 

 -eally, was in vogue ; and much of the night-soil produced in the 

 great manufacturing towns found its way back from these stagnant 

 receptacles to the land. 



But as the populations assembled in these industrial encampments 

 ^rew vaster and more dense, diseases of the so-called zymotir class 

 became more and more rife among them ; and though the respec- 

 tive causes of the several forms which zymotic or febrile disease 

 assumes remained unknown, it was gradually established by pro- 

 fessional investigations that they had all one common favoring 

 condition in the putrescent efiluvia of stagnant filth. 



To the few scientific inquir^^rs who traced out this relation, it 

 became apparent that the stagnant cesspool system was radically 

 Ticious, and must be rooted out at any cost. They perceived 

 that urban populations could only be preserved from febrile disease 

 by the daily removal of their ejecta before its entry into the state 

 of putrefaction ; and for this end a system of house and street 

 drains, kept constantly washed with abundant supplies of water, 

 seemed to aff'ord the readiest means. 



Here again the power of steam was on the side of progress. 



