CHEMISTRY 241 



nesium, and it is thought that the process of 

 reduction in the leaf may depend upon the 

 characteristic properties of this element ; at 

 all events, in organic chemistry, magnesium, 

 when employed in Grignard's reaction, is one 

 of the most effective agents to accomplish 

 reductions. 



In like manner, haemoglobin contains iron, 

 and the capacity of haemoglobin to unite 

 with oxygen, and as oxy haemoglobin to carry 

 it from the lungs to the tissues is unquestion- 

 ably due to the chemical behavior of that 

 metal. Other similar metallic elements, no- 

 tably copper in the class of compounds known 

 as haemocyanines, fulfill a similar function in 

 lower animals. 



Phosphorus in organic union is an essential 

 constituent of a great variety of the chemical 

 structures of living organisms, — the nucleic 

 acids, which appear to be not less important 

 than fats, carbohydrates, and proteids them- 

 selves in both animal and plant cells, contain 

 phosphorus as an essential constituent. Thus 

 phosphorus follows close upon nitrogen, after 

 carbon, oxygen, and hydrogen, as structural 

 material in biological chemistry. This same 

 element also occurs in many other compounds, 

 the simplest derivative of such bodies being 

 glycerophosphoric acid, 



