626 Professor Percy F. FranJcland [Feb. 19, 



of the nitrification-process over a period of four years in purely 

 mineral solutions, are strong presumptive evidence in favour of these 

 bacteria being able to gain a livelihood in the entire absence of 

 organic food-stufifs. I refrained, however, from promulgating such a 

 revolutionary doctrine until I should have had an opportunity of 

 repeating these experiments with materials in which the absence of 

 even the merest traces of organic matter had been assured, for as 

 chemists well know, even distilled water may contain traces of 

 organic matter. 



Such a rigid proof as I had contemplated has, however, in the 

 meantime been attempted by M. Winogradsky, also in connection with 

 his experiments on nitrification, and he has indeed found that the 

 nitrifying organisms flourish, multiply, and actually build up living 

 protoplasm in a solution from which organic matter has been most 

 rigorously excluded. Now this living protoplasm in the experiments 

 in question must have been elaborated by these bacteria from carbonic 

 acid as the source of the protoplasmic carbon, and from ammonia 

 and nitrous or nitric acids as the source of the protoplasmic nitrogen. 

 If these experiments are correct, and they were undoubtedly per- 

 formed with great skill and much caution, they are subversive of one 

 of the fundamental principles of vegetable physiology, which denies 

 to all living structures, save those of green plants alone, the power of 

 building up protoplasm from such simple materials. 



I had occasion to mention in connection with these nitrifying 

 organisms that they refuse to grow on the ordinary solid cultivating 

 media employed by bacteriologists, a fact which presents a great 

 obstacle to their isolation in a state of purity, for it is just by means 

 of these solid culture media that micro-organisms are most easily 

 obtained in the pure state. 



This difficulty has, however, been overcome in a most ingenious 

 manner, originally devised by Prof. Kiihne, in which the solid medium 

 is wholly composed of mineral ingredients, the jelly-like consistency 

 being obtained by means of silica. [Demonstration of preparation of 

 silica-jelly, consisting of ammonia sulphate, potassium phosphate, 

 magnesium sulphate, calcium chloride, magnesium carbonate, and 

 dialysed silicic acid.] 



Fixation of Free Nitrogen hy Plants. 



But whilst the study of the bacteria giving rise to nitrification has 

 thus led to the subversion of what was regarded as a firmly estab- 

 lished principle of vegetable physiology {viz. the incapacity of any hut 

 green plants to utilise carhonic acid in the elaboration of protoplasm)^ 

 the same science has received another shock of perhaps equal if not 

 greater violence through researches which have been carried on with 

 other micro-organisms flourishing in the soil. 



For nearly a century past agricultural chemists and vegetable 

 physiologists have been debating as to whether the free nitrogen of 



