PLANTS SUBJECT TO MICROBIAL DISEASES 291 



What effect does storage have upon the number of bac- 

 teria in properly hardened ice cream? 



What significance has a pure ice-cream supply in relation 

 to public health? 



11. Give results and conclusions in detail. 



REFERENCES 



SAVAGE: The Bacteriological Examination of Food and Water (1914), 



pp. 119-121. 



MARSHALL: Microbiology (1911), pp. 372-373. 

 WILEY, H. W.: Ice cream, Hygienic Lab. Bui. 56.' Milk and its 



Relation to the Public Health (1909), pp. 251-311. 

 HAMMER, B. W.: Bacteria and Ice Cream, Bui. 134 (1912), Iowa 



Agr. Expt. Sta. 

 MORTENSEN, M. and GORDON, J.: Lacto: a New and Healthful 



Frozen Dairy Product. Bui. 119 (1911), Iowa Agr. Expt. 



Sta. 

 WASHBURN, R. M.: Principles and Practice of Ice-cream Making. 



Bui. 155. Vermont Agr. Expt. Sta., pp. 9-10, 34-46, 53-54, 



64-66. 



BOLDUAN: Food Poisoning (1909), pp. 84-90. 

 AYERS, S. H. and JOHNSON, Jr., W. T.: A Bacteriological Study of 



Retail Ice Cream, Bui, 303 U. S. Dept. Agr., 1915. 



PLANT MICROBIOLOGY 



EXERCISE 1. TO DEMONSTRATE THAT PLANTS ARE 

 SUBJECT TO MICROBIAL DISEASES: INFECTION 

 OF CERTAIN SPECIES OF VEGETABLES HAVING 

 JUICY ROOTS, LEAVES, FRUITS, ETC., WITH B. 

 CAROTOVORUS 



Apparatus. Tubes of sterile 2% saccharose broth; 

 tubes of sterile agar; sterile water; sterile Petri dishes; 

 three sterile deep culture dishes; sterile filter paper; sterile 

 knife; sterile forceps; mercuric chloride, 1 : 500; juicy 

 vegetables. 



Culture. B. carotovorus (culture of high physiological 

 efficiency). 



Method. 1. The root of the carrot, turnip, rutabaga, 

 the cucumber or radish; the cotyledons of immature pea 



