BACTERIA IN ARTS AND INDUSTRIES 91 



inoculated into others by bees and other insects. Brown Eot 

 in tomatoes and potatoes is due to B. solanacearum, and 

 Cucumber Wilt is produced by B. tracheiphilus carried by 

 insects such as the potato-beetle. Black Rot in cabbages, 

 cauliflowers, and turnips, is due totheir invasion by.B. campestris, 

 a short motile bacillus which passes into and blocks the vascu- 

 lar channels in the leaf-stalks, stems, and roots, producing a 

 black discoloration with softening or rotting of the tissues. 



Many other bacterial diseases of plants are now known, and 

 for a description of these, reference should be made to the 

 important books by Erwin F. Smith, published by the Car- 

 negie Institute of Washington. 



Bacteria in the Arts and Industries Commercial 

 Bacteriology 



As we have seen in our introductory chapter (p. 17), present- 

 day bacteriology practically owes its origin to the work of 

 Pasteur upon Fermentation. We have already touched upon 

 the importance of bacteria in Agriculture, some organisms 

 being useful, others harmful to the growth of plant-life. The 

 scientific farmer must also know something of the many 

 bacterial and other diseases which may attack his stock, 

 and which help or hinder the work in his dairy. We have 

 already touched upon some of these questions incidentally in 

 other connections (the transmission of disease from animals to 

 man, and by milk, etc.), and we may here merely refer to the 

 part otherwise played by Bacteria in the milk-industry. 



Milk^Products : Butter-Making. It has long been known 

 that milk and cream from which the best butter is obtained 

 should be "ripened" for a couple of days before the butter is 

 made. This ripening is effected by the action of suitable 

 bacteria known as "starters." In the old-fashioned rough- 

 and-ready methods still mostly in use in this country, these 

 are left chiefly to chance and good luck, the milk and cream 

 being soured either by adding a little of last day's churning or 

 by leaving them to be inoculated with any of the stray organ- 

 asms with which the dairy teems. In other countries such 

 as America, Denmark, and Germany, where the applications of 

 scientific inquiry are more rapidly assimilated and put to a 

 practical use in the industries, and to a slight extent in this 

 country, such " starters " as are known to produce the best 

 results are now cultivated and added scientifically in order to 

 bring about this ripening, and different flavours can be pro- 

 duced in the resulting butter to suit the taste of the consumer. 

 Most of these starters are members of the Lactic Acid 



