ILLUSTRATIONS. 



PAGE 



PLATE I. Different forms of micro-organisms. To face . . 8 

 FIG. i A. A single " colony" of rod-shaped bacteria (bacilli) 

 growing on a plate of nutrient gelatine. The actual 

 diameter of this colony was about one fourth of an inch. 

 B. A cluster of the bacilli taken from the colony and 

 highly magnified . . . . . . . .13 



FIG. 2. The " plate method " of air analysis . . . .17 



PLATE II. Colonies of micro-organisms growing on dust 



particles. To preced,: . ... . . . .21 



PLATE III. Showing results of " plate analyses" of the air of 



different places in New York. To face . . ; .24 

 PLATE IV. Effect of sweeping on the number of micro-organ- 

 isms in the air. To face ...... 32 



FIG. 3. Ciliated cells from the large air-tubes of the human 



lungs, seen from the side ...... 39 



FIG. 4. Pigmentation of the lung from inhaled dust . . 44 



FIG. 5. Dust filters in the lung deeply pigmented . . .47 

 FIG. 6. Lymph filters (lymph-glands) at the root of the lung, 



the seat of local and healed tuberculosis .... 69 



