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 (Op % 
domesticated animals, such diseases as 7s S eA 
hog cholera, splenic fever, glanders, a 
black-leg, etc., are caused by Bacteria. 
The fighting of these forms, either to 8°) 
exclude, destroy, or neutralize them, is 
the business of modern medicine and iG 400 Gomewathes 
surgery. Besides the dangerous forms genic Bacteria. a, pus 
which attack animals, there are numer- cocci; }, erysipelas cocci; 
ous harmless forms constantly present ©% Bacteria causing diph- 
throughout the alimentary canal. theria; d, typhoid bacilli. 
: . xX 1500. Redrawn from 
Among plants the disease-producing fisher. 
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. 
Fie. 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 
