The question “which of the body cells are engaged in the production of antibodies” is not uncommonly asked. On physiological grounds it would not seem reasonable that the highly specialized tissues above mentioned could take up this work, even though they are the ones which suffer the greatest injury in disease. Hence it is to be expected that the lower or unspecialized cells are the source, and it has been shown that the antibodies are produced by the phagocytes (though not entirely as Metchnikoff maintained), by lymphoid tissue generally, by the bone marrow and also by connective-tissue cells, though in varying degrees. Since immunity depends on the activity of the body cells it is evident that one of the very best methods for avoiding infectious diseases is to keep these cells up to their highest state of efficiency, to keep in “good health.” Hence good health means not only _freedom from disease_ but also _protection against disease_. LIST OF LABORATORY EXERCISES GIVEN IN CONNECTION WITH THE CLASS WORK INCLUDED IN THIS TEXT-BOOK. Exercise 1. Cleaning glassware. Exercise 2. Preparation of broth medium from meat juice. Exercise 3. Preparation of gelatin medium from broth. Exercise 4. Preparation of agar medium from broth. Exercise 5. Potato tubes. Exercise 6. Potato plates. Exercise 7. Plain milk tubes. Exercise 8. Litmus milk tubes. Exercise 9. Sugar broth media. Exercise 10. Blood-serum tubes. Exercise 11. Inoculation of tubes. Action on complex proteins. Exercise 12. Production of gas from carbohydrates. Exercise 13. Production of indol. Exercise 14. Reduction of nitrates. Exercise 15. Chromogenesis: Illustrates nicely the variation with environment. Exercise 16. Enzyme production. Exercise 17. Making of plate cultures; isolation in pure culture. Exercise 18. Stain making and staining. Exercise 19. Cell forms and cell groupings. Exercise 20. Hanging drop slides. Exercise 21. Staining of spores. Exercise 22. Staining of acid-fast bacteria. Exercise 23. Staining of capsules. Exercise 24. Staining of metachromatic granules. Exercise 25. Staining of flagella. Exercise 26. Study of individual species. Exercise 27. Determination of thermal death-point. Exercise 28. Action of disinfectants on bacteria. Exercise 29. Action of sunlight on bacteria. DESCRIPTIVE CHART--SOCIETY OF AMERICAN BACTERIOLOGISTS. _Prepared by Committee on Methods of Identification of Bacterial Species.--F. D. Chester, F. P. Gorham, Erwin F. Smith._ _Endorsed by the Society for general use at the Annual Meeting, December, 1907._ GLOSSARY OF TERMS. AGAR HANGING BLOCK, a small block of nutrient agar cut from a pour plate, and placed on a cover-glass, the surface next the glass having been first touched with a loop from a young fluid culture or with a dilution from the same. It is examined upside down, the same as a hanging drop.