RETENTIOX OF ATOMS OF MATERNAL ORIGIN IN THE ADtLT WHITE MOT'SE 199 



was precipitated as magnesium ammonium phosphate. The precipitate 

 was filtered through an aluminium dish oi" 1.1 cm diameter having a 

 perforated bottom covered with filter paper. The dish containing the 

 precipitate was tlion plaoo(l unter the (Joiger counter. By comparing 



Table 1. — Wkight of 6 

 Nkw-bornt Offsprino of a Motsk 



the activity of an offspring killed at a given date with the activity of 

 another killed at a later date, it was possible to calculate what percentage 

 of the phosphorus atoms of maternal origin was lost in the interval 

 between the two dates. 



All offspring were killed successively, dissolved, and treated in the 

 way described above. The writer is much indebted to Mr. K. Zbrahn 

 for dissolving the mice and precipitating their phosphorus content. 

 All offspring were killed and investigated within about three months. 

 After the lapse of this time, the activity of the phosphate precipitates 

 had decreased so greatly that it could no longer be measured with suffi- 

 cient accuracy. The activity of the first offspring was compared with 

 that of the second, the activity of the second with that of the third, 

 and so on. 



The mouse obtains its ^-P content not only by birth but also by 

 lactation. In order to simplify the problem, to reduce the ^^P content 

 of the offspring mainly to such ^^P as was obtained by birth, the active 

 mother was replaced by an inactive mouse soon after gestation. As the 

 replacement of the mother was not made immediately after the birth 

 of the offspring, we actually measured the loss of ^^p acquired by birth 

 plus the ^^P acquired by lactation in the interval between birth and 

 replacement of the active mother by an inactive one, i.e. within a ftnv 

 days. 



