COXSERVATIOX OF SKELETAL CALCIUM ATOMS TIIROUCiU LIFE 229 



The fact that a very appiecial)l(5 percentage of the maternal phosphalc 

 is preserved ^though less than of the mal(M-nal calcium— is presumably- 

 due to the lower share of the hone ])h()sph()rus in the total body phos- 

 phorus than the part of bone calcium in body calcium. 17 per cent of 

 th{^ phosphorus content of the mouse are present in Ihe soft tissues, 

 but only 1 per cent of its calcium content is located there. The phosphorus 

 and calcium atoms present in various components of the soft tissues — 

 with the exception of desoxyribo nucleic acid phosphorus of some tis- 

 sues—are poorly conserved and, consequently, maternal calcium may 

 be expected to be better conserved than maternal phosphorus. 



From the fact that during the first 40 days of life — thus during a 

 phase of intense skeleton formation— only less than a third of the mater- 

 nal calcium atoms of the mouse is lost, we can conclude that the largest 

 part of the calcium atoms leaving the circulation is utilized to skeleton 

 formation and remains largely conserved in Ihe skeleton. 



Leblond and assoc.'"^ injected labelled phosphate into newborn 

 rats and followed the ^^p uptake by the humerus and the lower jaw. 

 Denoting the total ^^P taken up by the humerus in the course of the first 

 hour by 100, the uptake after eight hours was found to be 150, after 

 one day 117, and after three days 116. In spite of the rapid growth of 

 the humerus, the ^^p present after the lapse of a day is thus conserved 

 through the following days; similar results were obtained in investiga- 

 tions on the ^^P uptake by the lower jaw. 



The incorporation of calcium atoms in the rapidly growing bone tissue 

 can also be studied by following its uptake into the incisor of outgrown 

 animals. Carlson^"'"'"'^' ^'"^^ performed extensive and highly instructive 

 studies on the calcium metabolism of outgrown rats, among others 

 with the result that the calcium atoms incorporated with the rapidly 

 growing incisors are conserved to a very large extent in contrast to 

 those incorporated with the outgrown skeleton. 



It is rather difficult to determine the calcium intake and excretion 

 by the suckling mouse. Our adult mice (36 — 37 gm), however, were 

 found daily to consume 4 i 0.6 gm of standard bread containing 

 8.3 + 1- mgm. calcium; further 0.2 mgm calcium was contained in the 

 4 ml. of daily consumed water. The calcium recovered daily in the faeces 

 amounted to 8 mgm. A very appreciable part of the faeces calcium may 

 be assumed to be of endogenous origin, thus having passed th(^ circulation 

 before excretion. The share of endogenous phosphorus in the faeces 

 phosphorus was calculated from the specific activity of faces P and 

 urine (plasma) P*^^^''*^) these calculations lead to the result that 74 per 

 cent of the phosphorus of the human food and 72 per cent of the rat 

 food are absorbed into the circulation. About the same percentage of 

 the food P can be expected to be taken up by the mouse. As to the utili- 

 zation of calcium, data are available only for the uptake by luimans^^'\ 



