230 SPECIAL BACTERIOLOGY 



On Potatoes, a whitish coating. 



In Bouillon, a gelatinous sediment. 



CLADOTHRIX OCHRACEA (WINOGRADSKY). 



Found in water containing iron. Very like the C. dichotoma. For 

 its growth the water must contain carbonate protoxide of iron. By 

 oxidation an oxyhydrate of iron is formed, which is deposited in the 

 sheath and not in the threads of the organism. In water and under the 

 cover-glass, cultures can be obtained by the addition of iron salts. In 

 ordinary media the results are negative. 



BEGGIATOA. 



Found in water containing sulphuretted hydrogen. 



Microscopical Appearances. White threads without any distinct 

 cell membrane, enclosing in their interior dark grains of sulphur, formed 

 by the oxidation of the sulphuretted hydrogen. If a microscopical 

 specimen is prepared and the sulphur granules dissolved by adding alcohol 

 or bisulphide of carbon, a distinct system of transverse septa will be 

 visible in the threads. 



Biological Characters. It can be cultivated in water containing 

 sulphuretted hydrogen (also under the cover-glass), where active motility 

 and slow growth is observed. Flagella have, however, not yet been 

 demonstrated. Should the supply of sulphuretted hydrogen be 

 interrupted, then the small grains of sulphur in the threads are 

 gradually changed into sulphuric acid, when the threads appear 

 completely homogeneous. In time degenerative changes occur, vacuoles 

 being formed. The method by which the Beggiatoa increase is not 

 absolutely known. 



BACTERIA FOUND IN LEGUMINOUS NODULES. 



The earliest description of the leguminous nodules is by Malpighi in 

 his book published in 1687, in which he referred to them as galls, i.e. 

 diseased excrescences. In 1853, Treviraiius considered the nodules 

 normal growths. In 1866, Woronin discovered that there were 

 numerous entirely closed cells filled with living bacteria within these 

 nodules. In 1879* Frank showed that nodule formation did not occur 

 when the plants were grown in sterilized soil, thus proving that the 

 co-operation of soil bacteria was a necessary factor. In 1888, the true 



