IV 



illustrate in the most striking way that tenacity of purpose with 

 which he continued, to the very end of his life, the work he had begun 

 thirty-five years before. Not one of the numerous series of investi- 

 gations relating either to the internal or pulmonary exchange which 

 were undertaken during that period, failed in adding materially to 

 knowledge ; yet at the end of it the work was still going on. Thus 

 in the ' Arbeiten ' of the Leipzig laboratory for 1894, we find an 

 important research on the respiratory exchange in the abdominal 

 viscera as estimated by temporarily shunting them out of the circu- 

 lation, and another on the influence of grape sugar on the gases of 

 the blood — both characteristic examples of his method.* 



It will be seen from the preceding paragraph that Ludwig's 

 discoveries relating to circulation and respiration, depended largely 

 on his command of physical methods of research. In his equally 

 extensive and important investigation of the conditions which 

 regulate the functions of secreting glands, we have, along with 

 additional evidence of his unrivalled skill as an experimenter, 

 no less striking proofs that he was also a consummate anatomist. 

 The physiology of secretion occupied his attention throughout his 

 whole life. In 1842 it was the subject of the academical disserta- 

 tion which he presented to the University of Marburg on entering on 

 his career as a teacher ; and in 1889 we find him working with Nbvi 

 at a branch of the same question that he had discussed in his youth. 

 It is forty-five years since he undertook to investigate the funda- 

 mental question whether, when a gland is thrown by the stimulation 

 of its nerves into a state of activity while at the same time its supply 

 of blood is increased, the first effect is dependent on the second. An 

 experiment, remarkable for its extreme simplicity, settled the question. 

 Ludwig showed that in the head of a rabbit just severed from the 

 body, stimulation of the nerves of the salivary glands still determined 

 secretion, notwithstanding that there was, of course, no circulation. 

 Later, he proved, by an experiment on the same gland, that the process 

 of secretion, previously supposed to be one of "vital chemistry," could 

 be so transformed experimentally as to do external mechanical work, 

 and he thus established, between work-producing and secreting struc- 

 tures, a relation which had not before been thought of. 



It has been mentioned that the earliest of Ludwig's published 

 researches was on the physiology of the kidney. His prolonged 

 investigation of this subject illustrates, perhaps better than any 

 other, the scientific attitude of his mind. The adaptation of structure 

 to function is displayed in this organ in so striking a way, that from 

 the moment that its minute anatomy was successfully made out by 

 Bowman (1842), the teleological explanation which he gave was at 



* These two papers appear under the names of Professor Tangl and Dr. V". Harley 

 respectively. 



