PHYSICAL EESTOKATION IN TFSOATTT. 509 



to the tendencies of human action, as personified in himself, when 

 he said that " no grass grew where his horse's hoofs had trod." 

 The instances are few, wliere a second civilization lias flourished 

 upon the ruins of an ancient culture, and lands once rendered 

 uninhabitable by human acts or neglect have generally been for- 

 ever abandoned as hopelessly irreclaimable. It is, as I have 

 before remarked, a question of vast importance, how far it is 

 practicable to restore the garden we have wasted, and it is a 

 problem on which experience throws Httle light, because few 

 dehberate attempts have yet been made at the work of physical 

 regeneration, on a scale large enough to warrant general conclu- 

 sions in any one class of cases. 



The valleys and shores of Tuscany form, however, a striking 

 exception to this remark. The success with wliich human guid- 

 ance has made the operations of nature herself available for the 

 restoration of her disturbed harmonies, in the Yal di Chiana and 

 the Tuscan Maremma, is among the noblest, if not the most bril- 

 liant achievements of modern engineering, and, regarded in all 

 its bearings on the gi'eat question of which I have just spoken, it 

 is, as an example, of more importance to the general interests of 

 humanity than the proudest work of internal improvement that 

 mechanical means have yet constructed. The operations in the 

 Yal di Chiana have consisted chiefly in so regulating the flow of 

 the surface-waters into and through it, as to compel them to de- 

 posit their sedimentary matter at the will of the engineers, and 

 thereby to raise grounds rendered insalubrious and unfit for 

 agricultural use by stagnating water ; the improvements in the 

 Maremma have embraced both this method of elevating the 

 level of the soil, and the prevention of the mixture of salt-water 

 with fresh in the coast marshes and shallow bays, which is re- 

 garded as a very active cause of the development of malarious 

 influences.* 



* The fact that the mixing of salt and fresh water in coast marshes and 

 lagoons is deleterious to the sanitary condition of the vicinity, has been gen- 

 erally admitted, though the precise reason why a mixture of both should be 

 more injurious than either alone, is not altogether clear. It has been sug- 

 gested that the admission of salt-water to the lagoons and rivers kills many 

 ■fresh-water plants and animals, while the fresh water is equally fatal to many 

 marine organisms, and that the decomposition of the remains originates 



