MODERN BIOLOGY 413 



sciousness is; in regard to both these fundamental hypotheses science must 

 pronounce not only an "ignoramus," but also an " ignorabhnus." While this 

 statement was received with unreserved approbation in many quarters — 

 inter alia, by such a keen-minded thinker as Albert Lange — on the other 

 hand, it excited feelings of extraordinary bitterness on the part of radical 

 students of nature, headed by Haeckel. However, this subject, as also Du 

 Bois-Reymond's opinions regarding the theory of origin, belongs to the 

 next period and will be dealt with when the time comes to describe it. 



Karl Friedrich Wilhelm Ludwig appears by the side of Helmholtz 

 and Du Bois-Reymond as a pioneer in the field of exact physiology. He was 

 born at Hessen in 1816, studied at Marburg and Erlangen, and, having taken 

 his doctor's degree, spent some time in Berlin, where he joined J. Miiller's 

 circle, without, however, being included among his direct pupils. In 1846 

 he became professor of physiology at Zurich, and was called thence to Vienna 

 and later to Leipzig, where a new institute was founded for his benefit. There 

 he laboured for thirty years as a professor, gathering around him pupils 

 from all countries. He possessed rare powers of organization, which were 

 best displayed in the manner in which he arranged and guided his pupils' 

 work. In his earlier years he developed, with their assistance, a considerable 

 literary production; later on he preferred, modest as he was, to let his pupils 

 publish the ideas he suggested to them. Universally respected, he worked 

 with undiminished powers until the end; he died in 1895. 



Ludwig's original investigations primarily concern the functions of the 

 vegetative organs. Thus, he has explained the connexion between the secre- 

 tion of the salivary glands and the nerves that affect those organs; he investi- 

 gated the function of the heart in detail and analysed its various phases; he 

 experimented with the circulation of the blood and took valuable measure- 

 ments of its rapidity. Furthermore, he invented the graphic method, which 

 has since then played an important part in physiology. In a Lehrbuch der Phy- 

 siologic of the year i85x he summarized his views on the phenomena of life. 

 Characteristically enough, this work starts with a chapter on Physiologie der 

 Atome," which is really a survey of animal chemistry, while the following 

 chapter, "Physiologie der Aggrcgatzustdnde," deals with the phenomena of dis- 

 solution, diffusion, and currents. Consequently the functions of the different 

 organs are presented from a purely physical and chemical point of view, the 

 author's special subjects, the phenomena of circulation and secretion, natu- 

 rally receiving specially radical and expert treatment. Ludwig's teaching 

 was, of course, conducted on similar lines; through his pupils the conception 

 of vital phenomena here described spread to all civilized countries. 



Of radical importance for the development of biology was the fact that 

 the vital phenomena were thus explained by means of the same experimental 

 method that had been worked out earlier in physics and chemistry; it was 



