COMPOSITION OF MEDIA 43 
as being a rearrangement of the molecule. The composition of gelatin 
is indicated in Table V, which is taken from Mathews’ Physiological 
Chemistry. 
TABLE V 
SHOWING THE AMINO ACID CONTENT OF GELATIN 
Glycocoll... 20... .....0.05. 16.50 | Serine................. 0.40 
Alanine .........0..000. 0.80 Cystine............... 0.00 
Valine ....... 00. cece 1.00 Tyrosine... .........008 0.00 
Leucine..............06 2.10 Arginine.............. 7.62 
Proline... 2.0.2... 0.0005 eee 5.20 Histidine............. 0.40 
Phenylalanine........... 0.40 Lysine.............0.0. 2.75 
Aspartic acid. ........... 0.56 AMMOMNIA..........06. 
Glutamic acid........... 1.88 Tryptophane.......... 0.00 
The manufacture of gelatin has been described by Thiele (1914). 
He states that all varieties, whether used for bacteriological, photo- 
graphical or food purposes are made in about the same way. 
Agar. This according to Whittaker (1911) is derived from many 
plants, but principally from the genus ‘“ Gelidium”’ which grows 
on rocks along the coast of Japan. It is carefully cleaned by beating 
and washing. Finally it is dissolved and filtered to be late: dried in 
different shapes. Whittaker reports the composition of agar as shown 
in Table VI. Fellers (1916) found a remarkable uniformity upon anal- 
ysis of sixteen agars from very different sources. 
Taste VI 
CHEMICAL COMPOSITION OF AGAR-AGAR 
(After Whittaker, 1911) 
Crude 
. . Crud Carbo- 
Form. Quality. | Moisture. Fiber, protean hydrate. Ash. 
Slender............. No. l 13.10 0.47 2.21 80.34 3.88 
Best... 0... cc cee ee ee] we ee ee 14.39 0.35 1.49 80.17 3.60 
Powdered..........) 22-26. 11.39 | 2.62 3.58 74.91 7.50 
0. 
Chemically agar is a carbohydrate, a hexosan of the cellulose group 
of the polysaccharides. It is not used by bacteria. Very few instances 
are on record where agar was decomposed by a bacterial enzyme (see 
Smith’s Bacteria in Relation to Plant Diseases, 1905, p. 32). 
Reaction of Culture Media. Bacteria require an alkalin or neutral 
medium. This is an important factor in the growth of all microorgan- 
