Though manometric technique for respiration studies is a well standardized and often routine procedure, surprisingly little emphasis has been placed on standardization, i.e. method of propagation, duration of growth period, and subsequelit preparation of the test organisms whose respiration is being investigated. Stier and Stannard ( '36 a) showed that when cells of Saccharomyces cerevisiae are washed free of nutrients, their endogenous respiration continues at a readily measurable rate which depends upon the age of the culture. Giese ( '42)
found that the endogenous respiration of S. cerevisiae exhibits a decline with increase in age as well as with aeration after removal of the cells from their culture medium. Stier ('39) and Stier and Sprince ('41) demonstrated that after removal from their nutrient medium, aeration of cells of S. cerevisiae in Mil5 KH,PO, resulted in the production of suspensions exhibiting a lowered aerobic metabolism of dextrose. Stier and MacIntyre ( '42), using elaborate precautions in removing cells of S. cerevisiae from their culture medium, found an initial Qo, of 29.1 without substrate. After a precipitous decline, the rate assumed a value usually associated with a "normal endogenous " oxygen consumption.
While the foregoing work has made it clear that the endogenous respiration of S. cerevisiae declines with the age of the cells employed and that it is possible to alter the metabolic system in the cell by aeration of a suspension of cells, it has riot been demonstrated directly that the age of the cells has a n effect on their rate of oxygen consumption in the presence of extracellular subst rate. It should be recorded, however, that Stier and Stannard ('36a) made the brief statement that they observed a gradual fall in the initial rate of oxygen consumption to bc a function of the age of the culture when yeast metabolizes added Now with the Army of the United States.
' At present l e t Lt., Sanitary Corps, U. S. Army. 21 * Composition of the medium: KH,PO,, 2.0 gm. ; (NH,),SO,, 3.0 gm. ; CaCI,, 0.25 gm. ; MgSO,, 0.25 gm. ; asparagine (Difco), 1.50 gm.; glucose, 20.0 gm. ; Ractopptone, 2.0 gm.; yeast extrnct, 0.10 p.; distilled 11,O to make 1 liter. ' 1 7 0 48 15.77 26.5% 72 23.30 24.5%