LIST OF ILLUSTRATIONS 



FIG. . PAGE 



1. Forms of Bacteria 13 



2. Cocci 14 



3. Large Bacilli 14 



4. Small Bacilli 15 



5. Spirilla 15 



6. Spirilla 16 



7. Spores 16 



8. Spores 17 



9. Arrangement of Cocci 18 



10. A Streptococcus 19 



11. Bact. Anthracis 19 



12. A Tetracoccus 20 



13. Capsules 21 



14. Yeasts 27 



15. Spore-formation by molds 30 



16. A Plate Culture 39 



17. Effect of Acid on Bacteria and Yeasts 54 



18. Effect of Light 55 



19. Enzyme Action 57 



20. Etching of Marble by Plant Roots 88 



21. Effect of Nitrifying Bacteria on the Growth of Barley . 101 



22. A Septic Tank 112 



23. The Tile Drain of a Sewage Purification System . . . 115 



24. Nodules on Soy Beans 121 



25. Effect of Inoculation on Alfalfa 123 



26. Effect of Inoculation on Peas 126 



27. Effect of Inoculation on Sweet Clover 128 



28. The Cycle of Nitrogen 131 



29. A Section of an Udder 138 



30. Contamination from the Air 140 



xiii 



