720 BACTERIA IN AIR, SOIL, WATER, AND MILK 



tobacco fermentation is contributed by the leaf-enzymes, which, of 

 course, depend intimately upon soil and climatic conditions. 



Opium Productions. In the preparation of opium for smoking pur- 

 poses, the raw product is subjected to a prolonged period of fermenta- 

 tion by which the carbohydrates in the material are destroyed. Accord- 

 ing to various observers, the process is carried out in most cases by a 

 species of aspergillus. 



Indigo Production. Indigo, which is obtained from the plants 

 "Isatis tinctoria" and "Indigofer tinctoria," is not present, as such, 

 in the plants. In some of these it is found in the form of indican, in 

 others, as indoxyl. It has been shown by Alvarez that the oxidation of 

 indican and indoxyl into indigo-blue is carried out largely by bacterial 

 oxydases. Sterilized indigo plants do not produce the blue color. Alva- 

 rez 1 has isolated a bacillus closely related to the Bacillus mucosus 

 capsulatus group, to the action of which he attributes this oxidation. 



Bacteria in the Tanning of Hides. Raw animal hides are subject 

 to decomposition until treated by a process known as tanning. This 

 consists first in the depilation of the dried and salted skins, either by 

 partial putrefaction in an atmosphere saturated with water vapor or 

 by chemical treatment with solutions of milk of lime. After this, the 

 tanning proper consists in subjecting the skins to prolonged immersion 

 in solutions made up according to a large variety of formula? the 

 principle of all of which, however, seems to be found in the mixing of 

 various organic ingredients, such as bran-mash, oak-bark, and often 

 dried animal excreta, in which fermentation and acid production oc- 

 cur. According to Haenlein, 2 this acidification is the essential by 

 which the leather is sterilized and rendered soft. This author has 

 described the Bacillus corticalis, which he found in fir-tree bark and 

 to which he ascribes the acid fermentation of tanning liquors in which 

 this ingredient is employed. Wood, 3 who has worked extensively upon 

 the subject, has attempted to substitute pure cultures for the old un- 

 certain chance mixtures employed. In spite of these investigations, 

 however, while we must acknowledge the probable importance of bac- 

 teria in the tanning process, the subject is by no means on a scientific 

 or exact basis. 



1 Alvarez, Comptes rend, de Pacad. des sci., vol. 105. 



2 Haenlein, Cent, f . Bakt., II, i, 1895. 



8 Wood, Jour. Soc. Chem. Industry, 1895, 1899, 



