78 BACTERIOLOGY. 



chemical decomposition of the butter by the oxygen of 

 the air under the influence of sunlight and (2) through 

 fermentation by the lactic acid of the milk-sugar left 

 in the butter. Fats are, however, attacked by bacteria 

 when mixed with gelatin and used as culture media, 

 with the consequent production of acid. 



Putrefaction. By putrefaction is understood in com- 

 mon parlance every kind of decomposition due to bac- 

 teria which results in the production of malodorous 

 substances. Scientifically considered, putrefaction de- 

 pends upon the decomposition of complex organic 

 compounds, albuminous substances, and the like (glue, 

 albuminoid bodies), which are frequently first pepton- 

 ized and then further decomposed. Typical putrefac- 

 tion occurs only when oxygen is absent or scanty; the 

 free passage of air through a culture of putrefactive 

 bacteria an event which does not take place in natural 

 putrefaction very much modifies the process : first, 

 biologically, as the anaerobic bacteria are inhibited, 

 and then by the action of the oxygen on the products 

 or by-products of the aerobic and facultative anaerobic 

 bacteria. 



As putrefactive products we have peptone, ammonia 

 and amines, leucin, tyrosin, and other amido substances. 

 Oxyfatty acids, indol, skatol, phenol, and, finally, sul- 

 phuretted hydrogen, mercaptan, carbonic acid, hydro- 

 gen, and, possibly, marsh-gas (H 4 C). 



According to recent observations, nitrification is 

 produced by a small, special group of bacteria, culti- 

 vated with difficulty, which do not grow on our usual 

 culture media. From the investigations of Winograd- 

 sky it would appear that there are two common micro- 

 organisms present in the soil, one of which converts 



