62 MEDIA AND THEIR PREPARATION 
Starch Agar (McBeth, 1913). To 800 c.c. of boiling water add 10 
gms. of potato starch suspended in a little cold water. Concentrate 
by boiling to 500 c.c. This breaks up the starch grains and should give 
a nearly transparent starch solution. 
Starch solution.......... 0.0000 c cece eee ees 500 c.c 
AQAL.. ccc cee teen teenies 10 gms. 
Nutrient solution (same as for cellulose)... . 500 cc. 
SyntHetic Mepia 
Under the term synthetic the bacteriologist includes all media 
which may be prepared from pure chemical compounds. These may 
always be secured or brought to the same state of purity by the various 
methods well known to the chemist. The advantages of synthetic 
media are quite evident. 
1. They may be prepared in different lots which have a constant 
chemical composition. 
2. They may be prepared in different laboratories and render the 
data thus secured, more reliable. 
3. They lend themselves to the study of some one compound or 
element. For instance sulphur free media may be prepared to which 
certain sulphur compounds may be added. 
Parietti’s Solution. 
Carbolic acid, CcHsOH..................0.. 5 6.¢ 
Hydrochloric acid, HCl.................... 4c. 
Water... ce cc eee c cece ee eenees 100 c.c 
Drigalski and Conradi (1902) Medium. 
Dextrose (free broth)...................0.. 2000 c.c. 
Nutrose.. cece cece eee 20 gms. 
AQP. ce cece ence enee 40 gms 
Boil, dissolve, neutralize to phenolphthalein, autoclave at 120° C. 
for five minutes. 
Mayer’s Culture—Fluid (from Smith, 1905). 
Magnesium sulphate, MgSOz:7H2O......... 10 gms. 
Ammonium nitrate, NH4NO3............... 15 gms. 
Tribasic calcium phosphate, Cag(PO4)o....... 0.01 gms. 
Monobasic potassium phosphate, KH2PO4.... 10 gms. 
Distilled water............................ 1000 «.c. 
