Produced by Robert Rowe, Charles Franks and the Online Distributed Proofreading Team. THE STORY OF GERM LIFE BY H. W. CONN PROFESSOR OF BIOLOGY AT WESLEYAN UNIVERSITY, AUTHOR OF EVOLUTION OF TO-DAY, THE LIVING WORLD, ETC. PREFACE. Since the first edition of this book was published the popular idea of bacteria to which attention was drawn in the original preface has undergone considerable modification. Experimental medicine has added constantly to the list of diseases caused by bacterial organisms, and the general public has been educated to an adequate conception of the importance of the germ as the chief agency in the transmission of disease, with corresponding advantage to the efficiency of personal and public hygiene. At the same time knowledge of the benign bacteria and the enormous role they play in the industries and the arts has become much more widely diffused. Bacteriology is being studied in colleges as one of the cultural sciences; it is being widely adopted as a subject of instruction in high schools; and schools of agriculture and household science turn out each year thousands of graduates familiar with the functions of bacteria in daily life. Through these agencies the popular misconception of the nature of micro- organisms and their relations to man is being gradually displaced by a general appreciation of their manifold services. It is not unreasonable to hope that the many thousands of copies of this little manual which have been circulated and read have contributed materially to that end. If its popularity is a safe criterion, the book has amply fulfilled its purpose of placing before the general reader in a simple and direct style the main facts of bacteriology. Beginning with a discussion of the nature of bacteria, it shows their position in the scale of plant and animal life. The middle chapters describe the functions of bacteria in the arts, in the dairy, and in agriculture. The final chapters discuss the relation of bacteria to disease and the methods by which the new and growing science of preventive medicine combats and counteracts their dangerous powers. JULY, 1915. CONTENTS. I.--BACTERIA AS PLANTS Historical.--Form of bacteria.--Multiplication of bacteria.--Spore formation.--Motion.--Internal structure.--Animals or plants?-- Classification.--Variation.--Where bacteria are found. II.--MISCELLANEOUS USES OF BACTERIA IN THE ARTS. Maceration industries.--Linen.--Jute.--Hemp.--Sponges.--Leather. --Fermentative industries.--Vinegar--Lactic acid.--Butyric acid.-- Bacteria in tobacco curing.--Troublesome fermentations. III.--BACTERIA IN THE DAIRY. Sources of bacteria in milk.--Effect of bacteria on milk.-- Bacteria used in butter making.--Bacteria in cheese making. IV.--BACTERIA IN NATURAL PROCESSES.