December 9, 1904.] 



SCIENCE. 



783 



activity very soon becomes impaired and 

 consciousness is lost. Undoubtedly the un- 

 raveling of the mechanism of associated 

 memory is one of the greatest discoveries 

 which biology has still in store. 



VI. 



ELEMENTARY PHYSIOLOGICAL PROCESSES. 



It is, perhaps, possible that an advance 

 in the analysis of the mechanism of mem- 

 ory will be made when we shall know more 

 about the processes that occur in nerve 

 cells in general. The most elementary 

 mechanisms of self preservation in higher 

 animals are the respiratory motions and 

 the action of the heart. The impulse for 

 the respiratory action starts from the nerve 

 cells. As far as the impulses for the ac- 

 tivity of the heart are concerned we can 

 say that in one form at least they start 

 from nerve cells, and in all cases from 

 those regions where nerve cells are situ- 

 ated. But as far as the nature of these im- 

 pulses is concerned we know as little about 

 the cause of the rhythmical phenomena of 

 respiration and heart beat as we know con- 

 cerning the mechanism of associative mem- 

 ory. It is rather surprising, but never- 

 theless a fact, that physiology has not pro- 

 gressed beyond the stage of mere sugges- 

 tions and hypotheses in the analysis of 

 such elementary phenomena as nerve ac- 

 tion, muscular contractility and cell divi- 

 sion. Among the suggestions concerning 

 the nature of contractility those seem most 

 promising which take into consideration 

 the phenomena of surface tension. The 

 same lack of definite knowledge is found in 

 regard to the changes in the sense organs 

 which give rise to sensations. It is obvi- 

 ous that the most striking gaps in biology 

 are found in that field of biology which 

 has been cultivated by the physiologists. 

 The reason for this is in part, that the 

 analysis of the elementary protoplasmic 

 processes is especially difficult, but I be- 



lieve that there are other reasons. Medical 

 physiologists have confined themselves to 

 the study of a few organisms, and this has 

 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 cen- 

 tury. This turn is connected with a num- 

 ber of names, among which Liebig and 

 Pasteur are the most prominent. Agricul- 

 ture may be considered 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 proteins. 

 This gap was filled by Hellriegel, who 

 found that the tubercles of the leguminosfe, 

 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 syn- 

 thesis of its proteins. Winogradski sub- 

 sequently discovered that not only the 

 tubercle bacteria of leguminosse are ca- 

 pable of fixing the nitrogen of the air in 

 the soil in a form in which it can be util- 

 ized by the plant, but that the same can be 

 done by certain other bacteria, for in- 

 stance, Clilostridium pasteurianum. These 

 facts have a bearing which goes beyond the 

 interests of agriculture. The question of 



