SALTS 437 



thus be discussed from these two viewpoints — first as nutritive 

 media, then as physical systems. 



Possibly the first salt solution made for growing plants in 

 the laboratory without soil is that of the German botanist Sachs, 

 followed by the now better known one of Pfeffer. The latter 

 contains 



Ca(N03)2 0.8 gram KH2PO4 0.2 gram 



KCl O.'l gram FeCU Trace 



KNO3 0.2 gram Water 1 liter 



MgS04 0.2 gram 



Knop's solution for plant cultures is similar; it contains the 

 same compounds in the same proportions except that potassium 

 chloride is omitted and ferric phosphate is substituted for ferric 

 chloride. The American plant physiologist Shive has developed 

 the simplest of nutrient solutions; it contains but three salts — 

 calcium nitrate, potassium phosphate, and magnesium sulphate, 

 besides the usual trace of iron; it thus supplies the seven neces- 

 sary elements (in addition to carbon, hydrogen, and oxygen, 

 which are obtained from water and air). 



The almost perfect nutrient fluid for animals, at least for the 

 young of the same species, is milk. Except for its low iron 

 content, it contains the elements essential to animal growth. 

 Wright and Papish made analyses of milk using the spectro- 

 graphic method. A spectrographic record was obtained of the 

 dry matter in milk by burning and viewing it photographically 

 through a quartz spectrograph. The following elements were 

 found : 



The first six occur in large quantities; the remainder, only as 

 traces. Chlorine and iodine could not be confirmed by the 

 spectrographic method, but their presence had been adequately 

 established by other methods. 



This list, with a few additions, may be regarded as representing 

 the essential elements for animal life. Sulphur should be added. 



