. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 180 AUVEXTURES IX llADIUISOTOl'K llESEARCH Table 12. Weight of the fresh tissue in mgm ^\'eigl»t of ash in mgm % i>f the labelled I* found per mgm ash A I B C () in the course of 7 days only to a small extent. The figures in Table 12 cannot be compared directly with those obtained from fully grown animals for the following reason: the growing animal being much smaller the percentage of labelled P obtained for the same weight of the organ becomes larger; furthermore growth much fa
. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 180 AUVEXTURES IX llADIUISOTOl'K llESEARCH Table 12. Weight of the fresh tissue in mgm ^\'eigl»t of ash in mgm % i>f the labelled I* found per mgm ash A I B C () in the course of 7 days only to a small extent. The figures in Table 12 cannot be compared directly with those obtained from fully grown animals for the following reason: the growing animal being much smaller the percentage of labelled P obtained for the same weight of the organ becomes larger; furthermore growth much facilitates the uptake of phosphorus. We can, however, compare the ratio of the labelled P content of the incisor and of other organs; the value of this ratio for the tibia, for example, is found to be not appreciably different in the cases discussed above. As to the labelled phosphorus content of the blood, this amounted after the animal was killed to only per gram of blood; assuming a blood content of 10 cc. the circulation contained but of the labelled phosphorus administered of 5 days. THE EXCHANGE OF LABELLED PHOSPHORUS IN MOLARS In contrast to the incisors, molars of adult rats do not grow, so the labelled phosphorus found in the latter is due solely to exchange pro- cesses; the blood stream circulating through the molar carries labelled phosphate ions which enter into exchange processes with the calcium phosphate of the molar tissue. Such exchange processes also take place in the incisors simultaneously with the formation of new ossification })roducts. In the molars of adult animals, however, we encounter chiefly the former process; but though growth can be excluded we cannot discard the possibility of dissolution of tooth tissue at one place and a corresponding precipitation of calcium phosphate at another along the boundary between the circulating fluid and the tooth tissue. Small fluctuations in the acidity or parathormone concentration of the blood are suff
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