68 



BACTERIA IN RELATION TO PLANT DISEASES. 



Fig.59.f 



them.* Some of them are very sen- 

 sitive to the presence of acids, alka- 

 lies, strong alcohol, or antiseptics, or 

 their action is inhibited by the pres- 

 ence of other enzymes or of products 

 of enzymic fermentation in excess, or 

 by the absence of some combining 

 substance, such as lime or some weak 

 acid. Some do not pass readily 

 through the Chamberland filter or 

 through filter papers. Some are 

 destroyed at lower temperatures after 

 precipitation. Some are not pro- 

 duced except in presence of the sub- 

 stance which they can decompose, 

 but this is not true of all. Usually 

 an organism produces more than 

 one ferment and some bacteria are 

 known to produce five or six. Bac- 

 terium campestre produces at least 

 three and probably four, viz, diasta- 

 sic, cytohydrolytic, proteolytic, and 

 rennet. It also inverts cane-sugar, 

 but it is not yet known whether this 

 change is accomplished by means of 

 an invertase. On enzymes derived 

 from bacterial soft-rot organisms the 

 reader should consult recent papers 

 by Jones (Centralb. f. Bakt, 2 Abt., and 

 Vermont Exp. Sta. Rep.). Levy has 

 published an interesting paper on 

 " Some physical properties of en- 

 zymes" (The Jotir. Infect. Diseases, 

 Vol. II, 1905, pp. 1-48). 



For concentrating fluids in vacuo 

 at low temperatures (50 to 60 C.) 

 the thick-walled Kitasato flask shown 



*The same amount of dry heat does not affect them, and Loeffler has recently advised exposure 

 of thoroughly air-dried tissues and cultures to 150 C., dry heat, as an easy way of eliminating the 

 bacteria prior to grinding and extraction of the uninjured enzymes and other soluble products. 

 Non-sporiferous bacteria may be heated at 120 C. for 2 to 3 hours. Tissues and sporiferous bacteria 

 should be heated at 150 C. for one-half hour. (Deutsche Med. Wochenschrift, Dec. 22, 1904.) 



fFic. 59. ^Burettes used by the writer for titrating culture media. Twentieth-normal sodium 

 hydrate is used to determine the acidity, 'and the medium is finally brought to the desired alkalinity 

 with quadruple-normal sodium hydrate. The fluid is boiled and titrated hot, using phenolphthalein 

 as the indicator. The burettes should be graduated to tenths of a cubic centimeter and should hold 

 50 cc. Alkali should not be allowed to stand in them. 



