J. F. LOUTIT 



be the ^"Sr/Ca value in l)()nes of stillbirths, 1 S.U. should be the corres- 

 ponding figure for human plasma. (It would take al^out 20 litres of plasma 

 to make this assay feasible!) However, according to Bryant et al., the '•'"Sr 

 in stillbirths varies by a factor of about five so that the ^"Sr/^Sr ratio will also 

 vary widch' in stillbirths, in the respective plasmas of the mothers and in the 



mothers' diets. 



In summary, from stillbirths one learns more about the mother in the last 

 stages of pregnancy than anything else. Infants probably start post-natal life 

 with a variable »"Sr specific activity in terms of both ^Sr and calcium. 



Infants 



At birth there is the abrupt change from nutrition by maternal plasma via 

 the placenta to nutrition by maternal colostrum and milk. Infancy is a 

 period of great accumulation of calcium. The child's birth w^eight is doubled 

 in about six months and trebled in a year. Mitchell et al.^^ give the increase 

 in calcium as from 28 g at birth to 100 g in the first year of life. The increase 

 is accomplished in the face of numerous qualitative changes in diet — weaning 

 from breast milk to cow's milk, and the gradual introduction of mixed 

 feeding. Representative figures for cow's milk and mixed diets might be 

 300 [jLg and 1500 [xg ^Sr/g Ca. Very preliminary figures for human milk 

 suggest a value of about 200 [ig ^Sr/g Ca (personal communication from 

 G. E. Harrison). If this is confirmed an infant fed solely on breast milk 

 should have been supplied with »Sr and calcium in constant ratio from early 

 times to the institution of mixed feeding, but in post-natal life it has potenti- 

 alities for discriminating between strontium and calcium denied to it in 

 pre-natal life. It has a functioning gut and kidney. If, in fact, these organs 

 discriminate as in the adult, the Sr/Ca ratio in bone for both ^Sr and ^^Sr 

 could fall in the first few months of life. We cannot confirm this from available 

 analysis because of lack of clinical history. Infants fed on cow's milk will 

 have a rather higher intake of -"Sr and, if the milk is fresh or recently dried, 

 a much higher intake of '^^'Sr. (Much dried milk for infants in England has 

 been on the shelf for years and much comes from overseas.) Depending on 

 whether discrimination is yet established one would predict a smaller or 

 greater increase in the Sr/Ca ratios in bone. 



Since the diet in infancy varies, and since discrimination at this age is still 

 uncertain, it is inappropriate to derive an Observed Ratio (bone/diet) 

 certainly for ^Sr/Ca. However, if the infant's daily diet is relatively constant 

 in so far as ^^Sr/Ca is concerned— and this may be not far from the truth 

 once weaning from breast milk has occurred — one may speculate. Many 

 diets, either of cow's milk only or mixed, seem to contain at present about 

 5 [iiiC ^"Sr/g Ca and most infant bones contain about 1 [MJ-C/g Ca. From 

 this one may hazard the guess that the body's capacity to differentiate 

 between strontium and calcium does develop comparatively early. 



The growing child and adult 



The growing child eats substantially the same sort of diet as the adult. 

 He differs according to age on the quantity eaten. Whereas, the adult is 

 merely reforming bone at a slow rate of turnover, the adolescent is accumu- 

 lating calcium and its analogues for formation of new bone. Langham and 



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