2o8 SCIENCE PROGRESS 



phosphorus, maintained a high degree of resistance to certain 

 bacteria, which was totally lost when grown on the same soil 

 liberally manured with lime. This he attributed to the action 

 of the lime in liberating ammonia. 



The direct relation of the character of the cell-sap to the 

 question of immunity is also a well-ascertained fact, though 

 Laurent proved that the total acidity bore no relation to the 

 degree of resistance. Experiments showed that the resistance 

 of tubers of potato to bacterial invasion was due to soluble 

 substances which exist in the cell-sap and that the immunity 

 could be destroyed by subjection to alkaline solutions. In this 

 connection it is interesting to recall that in the attack of the 

 potato by Bacillus solaniperda Kramer found that the bacteria 

 first broke down the soluble carbohydrates with the production 

 of carbon dioxide and butyric acid, and in the first stage of 

 destruction the tuber shows an acid reaction. Later when the 

 proteids came to be destroyed ammonia, methyl- and trimethyl- 

 amine were formed, and after these bases had neutralised 

 the butyric acid the second stage of the disease was reached, 

 in which the tuber shows an alkaline reaction. The tubers rich 

 in sugar were more liable to attack than those rich in starch. 



The effect which a difference in chemical composition of the 

 plant-tissues can exercise upon the development of a virulent 

 form of parasitism is strikingly exemplified by Laurent's ex- 

 periments with different forms of ^. coli communis, B. fluorescctis, 

 B. enteridis, B. typhique, etc. All of these species were found 

 capable of living as true parasites on the potato after special 

 treatment had first diminished the resistance of the cells, the 

 typhus bacillus showing the most surprising results in power 

 of virulence. 



May we not consider that the different forms of Botrytis 

 raised by Kissling, as also the different forms oi B. coli communis 

 of Laurent, are " biologic forms " and that the foundation of 

 this theory was laid by Kissling in his work upon Botrytisl 



The past few years have been remarkable in considerably 

 extending our knowledge of parasitic diseases and in opening 

 out new avenues of research. The parasitism of bacteria has 

 been established equally with that of the fungi and much 

 confusion has been cleared away. But the mutual relationship 

 of these parasites in certain plant-diseases still demands atten- 

 tion and their action upon the living cell requires much further 



