560 



G. NICHOLS, JR. 



□ " 



or m a I 



P T E 



CIT R ATE = 



0.4 



3 



2 



Fig. 1. The mean accumulation per hour of H+, lactate", and citrate— ions 

 in the incubation medium surrounding fragments of cartilage-free metaphyseal 

 bone from 50- to 60-day-old mice. All data have been calculated in terms of 

 /xmoles accumulated per mg of alkali-soluble nitrogen ("cell nitrogen") present 

 in the system. Incubations were carried out for 2 hours in Kiebs-Ringer media 

 without Ca++ containing glucose 2 mg/ml buffered to pH 7.4 with bicarbonate 

 under a gas phase of 5 per cent COo and air at 37.5°C. H+ ion accumulation 

 was measured manometrically as CO2 displaced from the incubation medium. 

 Lactate and citrate were measured chemically. Note that the units on the 

 ordinate for citrate— are one-tenth those on the ordinates for the other two ions. 

 (Data in this figure have been replotted from Borle, Nichols, and Nichols, 

 1960a, and Borle, Nichols, and Nichols, 1960Z?.) 



(Dowse and Neuman, 1961; Kenny, 1961; Cohn and Forscher, 1962; 

 Deiss et ciL, 1962). All that remained, it seemed, was to establish 

 the relation between acid production and Ca mobilization, and 

 Schartum undertook to obtain the necessary evidence. Although the 

 details of his experiments have been published (Schartum and 

 Nichols, 1961a, 1961fo), I will review them briefly. 



The in vitro system seemed an excellent model, since Ca concen- 

 trations in the medium could be considered to bear a relation to 

 the bone fragments similar to that which the Ca concentration in 

 extracellular fluid bears to the skeleton in vivo. In preliminary ex- 



