BLACK-ROT OF CABBAGE 



347 



result of their direct attack upon the tissues, or of the poisons, 

 called toxins, which they excrete. They produce most of the 

 diseases of human beings, such as erysipelas, tetanus, diphtheria, 

 tuberculosis, typhoid fever, pneumonia, 

 cholera, etc. (Fig. 300). Among our 

 domesticated animals, such diseases as 

 hog cholera, splenic fever, glanders, 

 black-leg, etc., are caused by Bacteria. 

 The fighting of these forms, either to 

 exclude, destroy, or neutralize them, is 

 the business of modern medicine and 

 surgery. Besides the dangerous forms 

 which attack animals, there are numer- 

 ous harmless forms constantly present 

 throughout the alimentary canal. 



Among plants the disease-producing 

 Bacteria are almost as busy as among 



animals. Not only the tender herbaceous plants but even the 

 trees are attacked, and the loss caused every year is large. 



FIG. 300. Some patho- 

 genic Bacteria. a, pus 

 cocci; b, erysipelas cocci; 

 c, Bacteria causing diph- 

 theria; d, typhoid bacilli. 

 X 1500. Redrawn from 

 Fisher. 



FIG. 301. Potato tuber affected with the Potato Scab caused by a 

 Bacterium, Actinomyces chromogenus. From Bulletin 184, Vermont Agr. 

 Exp. Sta. 



Black-rot of Cabbage. This disease occurs on Cabbage, 

 Turnips, and other plants of this family. The Bacteria enter 

 through the openings of the leaf and advance through the 

 vascular bundles. They are able to destroy cell walls as well 



