Vitamins and Antivitamins 35 



multiply. Such substances, which may have been produced originally 

 by the faulty working of a single cell, would immediately be of 

 value to the organism, and would ensure its survival. It is not sur- 

 prising that in the innumerable generations through which they 

 must have passed in the course of ages, the micro-organisms have 

 been found effective chemical weapons for self-preservation. At one 

 time or another individuals which are faulty in some way may 

 produce unusual chemical compounds which may be of value in this 

 way. 



THE USE OF METALS BY LIVING CELLS 



For the want of a nail the kingdom was lost — Nursery Rhyme 



Vitamins are not the only minerals, besides the basic amino acids, 

 which are required in constructing the large molecules of living cells. 

 Life seems to have explored every possibility and has made use 

 somewhere or other of nearly every material available on the surface 

 of the earth. The common metals sodium, potassium, and calcium 

 are ubiquitous. There are a fair number of proteins which contain 

 other metals. Iron, for example, is an important constituent of 

 haemoglobin, the red protein of the blood of mammals. The iron, 

 present in a particular combination, enables the haemoglobin to pick 

 up oxygen in the lungs and to carry it into the tissues, where it is 

 released. Lobsters and other crustaceans offer a variation on the same 

 theme. Their respiratory protein contains copper instead of iron, and 

 as a result their blood is literally blue. 



Even more extraordinary is the fact that Ascidia (star fish) have 

 green, blue, and orange corpuscles in their blood, as well as colourless 

 ones. The coloured ones contain appreciable quantities of vanadium, 

 although its concentration in the sea water in which they live is so 

 small it cannot be detected by any known test. Other types of animal, 

 the beautiful annelid worms called SabelUds and SerpuUds, have 

 green blood, the colour of which is due to a haemoglobin-like protein 

 called chlorocruorin. 



Plant life uses the same kind of compound in chlorophyll — the all- 

 important pigment of green leaves — but the metal is now magnesium. 

 It might be thought that the difference represents the great division 

 between animal and plant life, the animals being based taking haemo- 

 globin or similar oxygen-carrying proteins and the plants using 

 chlorophyll : but as a matter of fact haemoglobin-like proteins have 

 been detected in the nitrogen-fixing nodules of leguminous plants. 

 So it would appear that both chlorophyll proteins and haemoglobins 

 were present before the division into plant and animal life took 

 place, but plants have relied increasingly on chlorophyll and many 



