32 A PRIMER OF BIOLOGY 



inflammable gas, hydrogen, now released from 

 combination. The compound formed by the union 

 of the potassium and oxygen, i.e., potash, is repre- 

 sented by the chemical formula KHO, hydrogen having 

 been ousted from its union with oyxgen and replaced 

 by potassium, represented by the symbol K. The 

 released hydrogen, combining with oxygen present 

 in the air, forms water once more. 



If we submit to chemical analyses the varied 

 organic compounds used by protoplasm as "food" 

 we find that they are relatively poor in oxygen, 

 although most of their constituent elements 

 are characterised by great affinity for it. The 

 combinations in which they find themselves, however, 

 interfere with their satisfying these affinities. They 

 are, so to speak, clogged and hampered by their 

 Deficiency neighbours, and cannot readily unite with the ele- 

 hf organic men t> ox yg en > so abundantly present in their vicinity 

 com- ' in the atmosphere. Let us look at a few examples, 

 pounds. rp^ re( j colouring matter of the blood, which is 

 known as haemoglobin, is a most complex body, 

 and its formula, according to one authority, is 

 C 600 H 960 FeN 134 S 3 O m , meaning thereby that there 

 are in the smallest possible particle or molecule of 

 the pigment, 600 atoms of carbon, 960 of hydrogen, 

 one of iron, 154 of nitrogen, 3 of sulphur, and 179 of 

 oxygen. There is thus not nearly enough oxygen 

 present to oxidise all these elements ; for to com- 

 pletely oxidise one atom of carbon two of oxygen 

 are needed ; one atom of oxygen is required to 

 oxidise every two of hydrogen, five of oxygen for 

 every two of nitrogen, three of oxygen for every two 

 of iron, and three for every one of sulphur. A 

 little elementary arithmetic shows us that to com- 

 pletely oxidise all the elements present in one molecule 



