60 ON THE SOURUK OF SULPHUR. 



and not animals, generate the constituents of blood containing 

 sulphur. When these are absent from the food given to an 

 animal, its blood cannot be formed. From this it also follows, 

 that vegetable food will be proportionally nutritious and fit to 

 sustain the vital processes of the animal body, according to the 

 amount of these ingredients contained within it. 



There also exist certain families of plants, such as the Cruci- 

 ferae, which contain peculiar sulphur compounds much richer in 

 that element than the vegetable constituents of blood. The seeds 

 of black mustard, the horse-radish, garlic, onions, and scurvy- 

 grass, are particularly marked in this respect. From all of these 

 plants we obtain, by simple distillation with water, certain vola- 

 tile oils, differing from all other organic compounds not contain- 

 ing sulphur, by their peculiar, pungent, and disagreeable odor. 



Those compounds containing sulphur are present in the seeds 

 of all plants, as well as in the plants themselves ; and as they 

 are particularly abundant in cultivated plants employed for 

 animal nutrition, it is quite obvious that a substance containing 

 sulphur is absolutely essential to the development of such com- 

 pounds, in order to supply to them their proper proportion of this 

 element. 



It is also obvious, that although all other conditions for the 

 nourishment of plants be present, if the compound containing 

 sulphur be either wholly absent or deficient in quantity, the vege- 

 table constituents containing sulphur will either be not at all 

 formed, or they will be generated only in proportion to the quan- 

 tity of the above compound. The air cannot contain any sub- 

 stances in which sulphur is present, unless indeed we except 

 minute and scarcely appreciable traces of sulphuretted hydrogen. 

 The soil, therefore, must be the only means of furnishing the 

 sulphur so necessary to the growth of plants ; and we are 

 ignorant of any way by which it can be introduced except 

 through the roots. 



The numerous analyses made of the water of mineral springs, 

 furnish us with a satisfactory explanation of the form in which 

 sulphur occurs in soils. The water of such springs is entirely 

 derived from the rain which falls upon the surface of the earth ; 

 the water percolating through the earth, dissolves all soluble 



