4 i 5 
Physiology of the Genus Eidamia. 
(b) The total growth in any case does not exceed that in the controls. 
(c) Increase in the growth-rate occurs, passing from the 0-5 to o-i per 
cent, concentrations. 
In both species growth in each member of the series is greater than 
that in the corresponding members of the tannic agar series, although from 
the point of view of the hydrogen-ion factor (taking into consideration the 
data obtained when other media with a similar pH range are used) the 
reverse result might be anticipated. 
It is worthy of note that practically no acceleration of growth occurs 
in any given member of the tannic and gallic acid series. This is probably 
due to the fact that there is no appreciable production of. ammonia (com¬ 
pounds of nitrogen would not exist except as impurities), hence change in 
the hydrogen-ion concentration through acid neutralization would not occur. 
E. Growth on Potato Extract Agar zvith Organic Acid in Various 
Concentrations . 
Numerous experiments were made with acid agars, using neutralized 
potato extract, employing methods of preparing the media and obtaining 
growth statistics similar to those already described (section II). Since the 
acid agar experiments have been described in some detail, the chief results 
are expressed in graph form : 
eta. 
Fig. 14. E. catenulata. Growth on potato extract agar with various concentrations of malic acid. 
I. Malic acid (Figs. 14 and 15) 2 per cent. = pH 2-4 ; 0*25 per cent. = pH 3. 
E. catenulata (Fig. 14). 
(a) The optimum growth takes place in the 2 and 1*5 per cent, con¬ 
centrations. 
(b) The growth-rate decreases progressively when passing from the 2 to 
o-i per cent, concentration. 
E e 2 
