THE METAMORPHOSES OF MATTER. 105 



fluids it was, until recently, always extracted.* Sulphur, too, 

 is so invariably present in the animal world, that chemical tests 

 can reveal its presence in the merest bit of feather, or scrap of 

 the oldest blanket. Eggs contain so large an amount of sul- 

 phur, that the presence of it is revealed by the silver egg- 

 spoon, which turns black (a well-known chemical function of 

 sulphur) under the natural operation for the performance of 

 which egg-spoons are made and appointed. A gas, holding 

 sulphur for one of its constituents (sulphuretted hydrogen), is 

 continually evolved from the hair, and hence the philosophy 

 of certain modern hair-dyes. Lead and lead compounds, bis- 

 muth and bismuth compounds, blacken, like silver and silver 

 compounds, under the influence of sulphur ; whence it follows 

 that, if litharge (oxide of lead) be made into a paste, and the 

 latter mingled with the hair, blackness follows. Silica, or the 

 matter of flint, is another curious constituent of vegetables and 

 animals. The shiny part of the stalk of grasses is nearly pure 

 silica, and the teeth of animals hold it in considerable pro- 

 portions. According to Decandolle, the violet and the vine 

 always contain gold in minute proportions ; and copper is said 

 to be an invariable constituent of tobacco. 



These examples will show how widely diffused, in small 

 quantities, are certain elements in living organisms. The 

 list might readily be extended; and perhaps in no case should 

 be closed without taking some cognisance of the curious me- 

 tallic elements potassium and sodium. Curiously enough, 

 though the metal now hardly a curiosity aluminium is a 

 constituent of clay, and perhaps of every variety of soil, no 

 vegetable or animal has ever yet been known to reveal alumi- 

 nium as one of the elements of its constituent organisation. 



Passing away from these, and many more curious con- 

 stituents of living beings, we find on near examination, as be- 

 fore announced, that carbon, oxygen, hydrogen, and nitrogen 

 constitute the great material staple of all things that, endowed 

 * For the present source of phosphorus see ante, pp. 13-16. 



