204 PHARMACEUTICAL BACTERIOLOGY 



rats. These microbic rat and mice exterminators have thus far proven 

 to be rather unsatisfactory. They have undoubtedly given excellent 

 results in some instances, and again they have been absolute failures. 

 The tests made by the University of California, and by Dr. Rupert Blue 

 in his famous plague-rat extermination in San Francisco, have given 

 almost wholly negative results. A microbic squirrel exterminator 

 (" squirrelin ") has proven entirely unsatisfactory. 



When we consider how difficult it is to prevent fatal epidemics, it cer- 

 tainly does seem reasonable to suppose that it should be a comparatively 

 easy matter to find ways and means for disseminating fatal epidemics, but 

 so far the commercial attempts made in that direction have proven rather 

 discouraging. Further carefully conducted experiments along this line 

 are necessary. It is known that the ravages of certain pests are sometimes 

 suddenly checked by the natural invasion of some pathogenic organisms. 

 This is frequently observed among plant lice (Aphis) and other insect 

 enemies of plants. 



6. BACTERIA IN THE TANNING INDUSTRY 



The object in tanning leather is to protect it against decomposition and 

 to render it pliable. The various animal hides reaching the tannery 

 are preserved by drying and salting. At the tannery the hides are treated 

 as follows : 



A. Removing the Hair. Depilation. This is done by means of chemi- 

 cals, as lime or sodium sulphite, or through the agency of rotting bacteria, 

 as Bacillus (Proteus) vulgaris and others. Just which of several species 

 of rotting bacteria is most active in this process has not been definitely 

 determined. i 



B. Drenching or Baling. After the hair has been removed, the hides 

 are macerated in an aqueous solution of the excrement or dung of pigeons, 

 hens and dogs. These substances set up a lactic acid fermentation due to 

 the microbes contained therein. The active organisms have not been iso- 

 lated as yet; Bacillus gasoformans and B. erodiens are perhaps active, but 

 there are also present many yeasts, moulds and other organisms which may 

 have their special effects. 



The first part of this process, known as "bating," is initated by bird 

 dung; the second process, known as "puring," is due to the action of 

 dog dung. Attempts have been made to use pure cultures of the active 

 microbes to supplant these filth substances, but so far these efforts have 

 not proven wholly successful. 



C. Tanning. The bated hides are next treated in the tan pit (coarse 

 skins) or in bark liquor (soft thin skins), where the souring process takes 

 place. This process is also due to bacterial activity. Our knowledge of 



