624 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



less also are a number of Bacteria found on the mucous membrane of the mouth. 

 On the other hand, many are associated with definite diseases. Spirochcete Ober- 

 meieri (fig. 368^) is found in the blood in great quantities during relapsing fever; 

 Bacillus anthracis (figs. 368 *" and 368^) causes anthrax in cattle, &c.; and a great 

 many other diseases — diphtheria, cholera (figs. 368 ^ and 368 *"), tuberculosis, leprosy, 

 &c. — are associated with the activity of specific bacterial organisms. Nor must we 

 omit to mention the numerous forms which occur in the soil, some of which are 

 concerned in the process of nitrification, i.e. which oxidize ammonia into nitric acid, 

 thus rendering this source of nitrogen available to higher plants, whilst others 



Fig. 368.— Bacteria. 



1 The "'blood-portent," Micrococcus prodigiosus. 2 Zoogloea-form of same. ^Bacterium aceti. * The same more highly 

 magnified, s Spirochcete cholerm asiaticce. 6 The same more higlily magnified. ' Bacilhis anthracis and red blood- 

 corpuscles, s xhe same more highly magnified. 9 Spirochcete Obermeieri and red blood-corpuscles. 10 Sarcina ventriculi. 

 1. 2, s, s, 7, 9 X 300; 10 X 800; *. 6, s x2000. 



actually fix free nitrogen, as is the case with the organism occurring in the root- 

 tubercles of many leguminous plants (c/. p. 521). There is no doubt this organism 

 (Rhizohiutn, as it has been called) can store up free nitrogen, and that leguminous 

 plants, when associated with it, obtain nitrogen not to be accounted for as combined 

 nitrogen obtained from the soil. Curious also is the activity of the sulphur and 

 iron Bacteria. The former (e.g. Beggiatoa alba) have the power of reducing the 

 sulphates contained in the waters which they inhabit and of storing up sulphur- 

 grains in their protoplasm; whilst the latter (e.g. Crenothrix Kühniana), not 

 uncommon in water-pipes, where they often develop in enormous quantities, store 

 up iron in the gelatinous sheaths of their filaments. 



That Bacteria existed in former times, and were then, as now, the agents of 

 decomposition, seems probable in view of the condition revealed by residues of dead 



