142 TRACE ELEMENTS IN ANIMALS 



Again, determinations of the copper content of the blood do 

 not reveal any correlation between copper content of blood and 

 incidence of sway back. Certainly Bennetts and Chapman (1937) 

 in Australia found particularly low values for the copper content 

 of the blood of four ewes that gave birth to affected lambs (less 

 than 0-01 mg. per cent). On the other hand, Innes and Shearer 

 (1940) found that in Derbyshire the average copper content of 

 the blood of ewes giving birth to swayback lambs was 0-058 mg. 

 per cent, while the value with ewes on swayback farms bearing 

 normal lambs was actually somewhat lower, namely 0-045 mg. 

 per cent, but in both groups there was quite a wide range of 

 values, 0-037-0-070 mg. # per cent in the swayback group and 

 0-034-0-061 mg. per cent with the ewes bearing normal lambs. 

 Higher mean values were found for the copper content of the 

 blood of ewes in non-sway back areas, but the range was even 

 wider than in affected areas. There was thus no indication of 

 any close relationship between copper content of the blood of 

 the ewes and the incidence of swayback. This conclusion is 

 supported by the results of the examination by Eden (1939, 

 1941) of the blood of more than 300 sheep in an area of Northum- 

 berland where swayback is unknown. Here very wide variations 

 in copper content were found, the mean value for ninety-four 

 sheep examined in 1940 being 0-080 mg. per cent with a range 

 of 0-013-0-210 mg. per cent. Eden also points out that the 

 pastures in this Northumbrian area have an even lower copper 

 content (6-10 p.p.m. of the dry weight) than those of the sway- 

 back area of Derbyshire. It may be concluded that much work 

 requires to be done to put our knowledge of the effects of copper 

 deficiency in animals on a firm basis. 1 



The Effect of Iodine Deficiency. Iodine deficiency is gener- 

 ally regarded as the cause of goitre in man and other mammals. 

 Goitre results from enlargement of the thyroid gland which 

 contains the characteristic protein thyroglobulin, one of the 

 constituent amino-acids of which, namely thyroxine, contains 



1 In a paper which appeared since the above was written Shearer 

 and McDougall (1944) express the opinion that the Australian disease 

 is due to an uncomplicated deficiency of copper in soil and herbage 

 but that in this country this is not so although affected animals suffer 

 from copper deficiency. 



