15. _B. coli commune_ " 88 16. _B. erodiens_ (Becker) " 97 17. Plate culture from fresh puer " 97 18. " " puer wheel " 103 19. _B. putrificus_ " 103 20. Organisms in pigeon dung, × 1000 104 21. Pure culture of bacillus (_d_) from sweated skin _facing_ 106 22. " " " (_e_) " " " 106 23. _B. butyricus_ (Hueppe) " 112 24. _Spirillum volutans_ (Kutscher), stained to show flagellæ " 112 25. " " " unstained preparation " 112 26. Curves showing rate of hydrolysis 129 27. Organisms in bran drench, × 1000 240 28. Chains of bran bacteria, × 1000 240 29. Bran fermentation, advanced stage 241 30. _B. furfuris_, α _facing_ 269 31. _B. furfuris_, β " 269 32. Cultures of α in glucose gelatin 268 33. Gas curve (_B. furfuris_) 277 PREFACE The present volume is the outcome of a desire to preserve the numerous notes which I have made during over twenty years’ work at the practical and scientific study of bating. It has been my wish to complete the investigation of this important process in leather manufacture, for, as Lord Allerton has paradoxically remarked:[1] “Good leather is made before the skins go into the tan liquor at all,” but owing to circumstances having drawn me more and more to the commercial side of the business, I have been compelled to abandon this project. [1] Report of First Conference of Leather Trade Chemists, 1897, p. 146. When learning the trade as an apprentice every fault in the leather was attributed to this part of the work, and the troubles and miseries of the “puer shop” first caused me to take up the study of puering. I was determined to know the causes underlying the process. Puering is not only a filthy and disgusting operation, but is prejudicial to health, and in the nature of it is attended by more worry and trouble than all the rest of the processes in leather making put together. By giving a résumé of the work done up to the present time, I hope to be of assistance to the younger generation of Tanning Chemists, to some of whom is reserved the privilege of carrying on the work.