180 SIR ARNOLD TIIEILER 



strueted for the wliole year. In May 1919, 40% of the 

 control stock were eating bones, this number slowly in- 

 creased till in Augnst it reached 80%. In August and 

 September the grass began to grow, and the degree of 

 pica diminished slowly up to October, when after the first 

 rains, the curve suddenly dropped to 5%, that is to say 

 only 5 out of the 100 animals were still eating bones. So 

 long as the grass was luxurious the number remained 

 low, but at the end of November the grass wilted and the 

 curve rose witliin three weeks up to 85% . During Decem- 

 ber and January the number remained equally high, 

 except at the end of January, 1920, after the heavy rains 

 in Bechuanaland, when it fell for a little while to 50%. 

 Chemical analyses of the pasture grasses during the same 

 period brought out the important fact that when the bone 

 craving is acute the amount of phosphorus is low ; and a 

 curve showing the phos^jhorus content of the grass dur- 

 ing the period showed that it was in inverse ratio to the 

 degree of pica. From this it may be concluded that 

 hone-craving is caused hy a lack of phosphorus in the 

 food. 



This was further corroborated by bringing a num- 

 ber of cattle from Pretoria; these had no bone craving, 

 but after 7 weeks grazing on Armoedsvlakte 65% were 

 afifected with pica. When the bone cravers were turned 

 into the stable and fed on the usual stable food, pica 

 disappeared within a few weeks; if tlie same animals were 

 again turned out on the veld they again developed tlie 

 craving. This was not due to grazing on any particular 

 variety of grass : a number of different grasses were 

 tested separately, but all with the same result. 



It was known that bone-cravers lost the craving within 

 a few weeks when fed on mealie-meal, bran and lucerne 

 hay, but it had not been proved which of the three in- 

 gredients of this fodder was responsible for tliis result. 

 Mealie meal and lucerne were tried, without result, but 

 the addition of 2 lbs. of bran to each dav's ration made 



