132 



Claude A. Villee 



and thirty-three earlier placentas, ranging in age from 6 to 37 

 weeks. The decrease in oxygen consumption with age is linear 

 until a gestational age of about 30 weeks, after which the Q 0j 

 (microlitres of oxygen utilized per mg. of dry weight of tissue 

 per hour) is relatively constant until term (Fig. 1). The values 

 for oxygen consumption reported here are slightly lower than 

 those reported by Hellman, Harris and Andrews (1950), 

 probably because of the differences in the method of determin- 

 ing the dry weight of the tissue. In their experiments the 

 tissue was removed from the medium at the end of the incuba- 

 tion period, dried and weighed. We have found that the wet 

 weight of the tissue recovered at the end of the experiment is 

 only 60 to 70 per cent of that put in originally. To avoid this 

 source of error, the dry weight : wet weight ratio for each 

 placenta was determined from adjacent slices. The placental 

 slices recovered from the incubation medium at the end of the 

 experiment were weighed and their glycogen content was 

 measured. The ratio of dry to wet weight of the placenta 

 almost doubles during gestation (Fig. 2). 

 15 



12.5 



10 



* 7.5 



5- 



• • 





\0 



20 



25 



30 



35 



40 



WEEKS OF PREGNANCY 



Fig. 2. The ratio of dry to wet weight of the placenta as a function of placental 

 age. The arrow at 40 weeks indicates the range of the values obtained for 



term placenta. 



