36 Inside the Living Cell 



of them have lost abihty to make haemoglobin-hke proteins. 



Enzymes have also been isolated which contain copper, zinc, 

 manganese, iron, and vanadium. The amount of the metal in the 

 enzyme is usually quite small, less than 1 per cent, and as only small 

 quantities of the enzymes are present in the tissues, the amounts of 

 the metals used in this way are very small — mere traces are sufficient 

 to satisfy the needs of organisms. Living things usually get what they 

 need without any difficulty, but sometimes the supply falls below 

 the level required. 



It has been found in experiments with plants growing in carefully 

 purified solutions, that iron, manganese, boron, copper, and zinc are 

 essential for plant growth, at concentrations of less than one part in a 

 million. No more than this is necessary, and much larger quantities 

 may be harmful. If the soil is seriously deficient in any of the metals, 

 plant growth suffers, but it can be improved by making good the 

 deficiency. Thus, the application of manganese and zinc compounds 

 to marshland fields in Kent increased the yield of potatoes from 

 seven to eleven tons per acre. In south-east Australia there is an 

 extensive coastal strip in which a copper deficiency limits vegetation. 

 Oats, wheat, and lucerne all failed without added copper, but grew 

 luxuriantly when a copper salt was added to the soil. Further inland, 

 zinc is also needed, but extra copper was also required before the 

 clover would set seed. It has been found that plants often grow quite 

 well without much copper up to blossoming time, but seed formation 

 is interfered with. The effect of copper on clover growth is greater if 

 the copper salt is applied a season in advance, due apparently to its 

 effect on nitrification bacteria. Fruit trees, which will not fruit, have 

 been made to do so by inserting capsules of a manganese salt into 

 holes bored into the trunks. 



Even when plants can grow well, they do not always satisfy the 

 mineral requirements of the animals feeding on them. Diseases due to 

 cobalt — and copper — deficiencies in sheep and cattle are well known 

 in various regions. In Scotland and Australia sheep *pining' occurs 

 on soils with less than five parts per million of cobalt. It has been 

 found that this condition is remedied if cobalt, together with copper, 

 in the form of salts, of course, is added to the food. Apparently only 

 ruminants suffer from this deficiency; horses, kangaroos, and rabbits 

 do quite well under the same conditions. 



Copper is utilized, rather oddly, in putting the 'crimp' into sheep's 

 wool. If the herbage is deficient in copper, the wool grows straight. 

 The reason, apparently, is that the molecules of the wool protein are 

 first formed in a straight parallel form. The 'crimp' is produced 

 when the long protein chains are joined by -S-S- bonds, an operation 



