42 MEDIA AND THEIR PREPARATION 
Acidity: 
N/10‘NaOH. 2... ce ec eee 9.04 
As lactic acid... ce ccc ce cece eee ee 8.13 
Nitrogen as: 
Total... 0.0. cece eee eee eens 9.07 
Insoluble and coagulable................... 0.19 
Proteoses... 0.000. cece ne eee ees 2.01 
Peptones.... 0.00.0... c ccc eee ee eee eee 2.68 
Total meat bases..........0 0... .c ce eee eee 3.82 
Creatin and creatinin................00005. 1.14 
Xanthin baseS........ 0.0.0. ee cee eee eee 0.03 
Meat bases other than..................... 2.65 
AMMONIA... eee eee 0.37 
Ether extract... 0000000000. eee ce ee cece ees 0.94. 
Undetermined... 0.0.00... c eee eee eee 5.89 
Net weight........ 00.00.00. cece cece eee ens 57.80 
TaBLe IV 
PARTITION OF THE NITROGEN OF MEAT EXTRACTS 
(Cook, 1908) 
PerRcentaGe or Torat NITROGEN. 
Variety 
Total Total Nitrogen Nitrogen | Nitrogen AMINO NITROGEN, 
Pee [Ammonia Creati- Purine | 12 Phos- ("sn acid jin Tannin 
ber. er | Nitrogen.| ,7.74 Nitrogen.| Photung-| Alsohol | Salt Van 
Cent. Nitrogen. stic Acid Filtrate, | Filtrate. Formol Slyke 
, : ] 
Filtrate. Method. Method. 
ee eeeatlineemmmnmmiaen haan simnentted iieetimtbemmnineae cenbiiemernaimenaiennien™ Tagianeemestmmenametsemintina: seneedl tepeadebnoneimmme: dmmmemmatenmetreiniien  iuinem shinies cimmenonentanem semen | Kemmniinatimmmeneiiinammemsemeiiel Shnmaieeshadindinamméneeninmenmnndl Lammemmeniasiiarinaiienmemenesian’ Lamammnnmmmmemettiammmntendl locanmmnsninernanenen aman rad 
1 9.56 | 2.62 | 22.49 | 3.385 | 7.64) 78.04 | 54.91 | 10.94 | 18.50 
2 9.65 | 2.49 | 22.59 | 3.52 | 6.84 | 78.45 | 55.85 | 10.94 | 18.23 
3 7.68 | 1.56 | 32.42 | 2.86 | 71.35 |100.00 ; 73.04 | 10.63 | 15.63 
4 49.74 | 76.73 | 59.87 | 10.27%) 15.54 
bene 89.19 | 64.21 | 9.53 | 17.89 
* No correction for ammonia; no determination. 
Gelatin. This was first used by Koch as a solid medium. Since 
that time it has become firmly established in the bacteriological labora- 
tory. It has the advantage over some other substances used in solid 
media of allowing a larger number of colonies but the great disadvantage 
that it is a bacterial food and may be liquefied. This often causes a 
loss of plates. 
Gelatin is made from collagen, a constituent of white fibrous tissue. 
Emmett and Gies (1907) explain the formation of gelatin from collagen 
