66 ISOLATION AND CULTIVATION OF ANTAGONISTS 



tract or corn steep liquor was added and brown sugar was used in place 

 of glucose, the growth of the organism and the production of penicillin 

 were greatly facilitated (5, 281). The ratio of C and N sources is sig- 

 nificant. It has been shown, for example, that penicillin is produced 

 in organic media when the ratio sucrose-peptone is less than i .0, and in 

 inorganic media when sugar-NaNOg ratio is i.o or lo.o (591). 



The following was found (838) to be a suitable medium for maxi- 

 mum production of penicillin : 



Lactose 40.00 gm. 



NaNOg 3.00 gm. 



MgS04.7H20 0.25 gm. 



KH0PO4 0.50 gm. 



ZnSOg 0.0 1 gm. 



Corn steep liquor 90 ml. 

 Distilled water to make 1000 ml. 



This medium has been variously modified, as by reducing the lactose 

 to 20 mg. per liter and the corn steep to 40 ml. or by using in its place 

 25 mg. of dried steep liquor solids (764). 



The need for a specific penicillin-promoting substance, such as might 

 be found in corn steep or in other plant extracts (555)j in order to in- 

 crease appreciably the yield of the antibiotic agent is of particular in- 

 terest. Certain amino acids, namely, arginine, histidine, and glutamic 

 acid, in concentrations of 0.3, 0.3, and 0.4 gm. per liter, respectively, 

 appear to provide a large part of this stimulating effect (1004). A 

 proper balance of the concentration of the ions POf , SOf , NO -3 , 

 and Mg+-^ is also essential. The proportions of the essential three salts 

 in optimum solution were found (733) to be KH2PO4 — O.475, 

 MgS04.7HoO— 0.05, and NaN03— 0.475 j different strains show 

 marked differences in their response to a change in balance of these 

 three salts. 



This led to the development of different synthetic media, such as the 

 following (735) J the amounts are given on a liter basis: 



Starch 5.0 gm. 



Lactose 25.0 gm. 



Glucose, crude 5.0 gm. 



