RECENT DEVELOPMENT OF BIOLOGY 21 



had the effect that for the last fifty years the same work has been 

 repeated with slight modifications over and over again. 



VII. Technical Biology 



I think the creation of technical biology must be considered the 

 most significant turn biology has taken during the last century. 

 This turn is connected with a number of names, among which Liebig 

 and Pasteur are the most prominent. Agriculture may be con- 

 sidered as an industry for the transformation of radiating into chem- 

 ical energy. It was known for a long time that the green plants were 

 able to build up, with the help of the light, the carbohydrates from 

 the carbon dioxide of the air. Liebig showed that for the growth of 

 the plant definite salts are necessary, that these salts are withdrawn 

 from the soil by the plants, and that in order to produce crops these 

 salts must be given back to the soil. One important point had not 

 been cleared up by the work of Liebig, namely, the source of nitrates 

 in the soil which the plants need for the manufacture of their pro- 

 teins. This gap was filled by Hellriegel, who found that the tubercles 

 of the leguminosse, or rather the bacteria contained in these tubercles, 

 are capable of transforming the inert nitrogen of the air into a form in 

 which the plant can utilize it for the synthesis of its proteins. Wino- 

 gradski subsequently discovered that not only the tubercle bacteria 

 of leguminosse are capable of fixing the nitrogen of the air in the 

 soil in a form in which it can be utilized by the plant, but that the 

 same can be done by certain other bacteria, for instance, Chlostri- 

 dium pasteurianum. These facts have a bearing which goes beyond 

 the interests of agriculture. The question of obtaining nitrates from 

 the nitrogen of the air is of importance also for chemical industry, 

 and it is not impossible that chemists may one day utilize the ex- 

 perience obtained in nitrifying bacteria. 



With the discovery of the culture of nitrifying bacteria we have 

 already entered the field of Pasteur's work. Yeast had been used for 

 the purposes of fermentation before Pasteur, but Pasteur freed this 

 field of biology just as much from the influence of chance as Liebig 

 did in the case of agriculture. The chemist Pasteur taught biologists 

 how to discriminate between the useful and harmful forms of yeast 

 and bacteria, and thus rendered it possible to put the industry of 

 fermentation upon a safe basis. 



In recent times the fact has often been mentioned that the coal 

 fields will be exhausted sooner or later. If this is true, every source 

 of available energy which is neglected to-day may one day become 

 of importance. Professor Hensen has recognized the importance of 

 the surface of the ocean for the production of crops. The surface 

 of the ocean is inhabited by endless masses of microscopic organisms 



