September 15, 1916] 



SCIENCE 



371 



diffusion and osmosis. The exactness of 

 the results were recognized by Ostwald. 



He never lost interest in the original 

 problem and a number of his students were 

 assigned various phases of it during the 

 succeeding years. An evidence of his open- 

 mindedness is the fact that he was not dis- 

 turbed by results which seemed to oppose 

 his original view. 



How Ludwig would have reveled in the 

 clever technique displayed in the models 

 and drawings of the kidney tubules, which 

 have been developed in this laboratory by 

 Dr. Huber. 



Although emphasizing the important 

 part played by blood pressure in the secre- 

 tion of the urine, he proved experimentally 

 that the pressure of the blood does not ex- 

 plain the secretion of the saliva, and his 

 epoch-making discoveries with regard to 

 the activities of the salivary glands began 

 a new era in our knowledge of secretion 

 processes. He proved that gland cells, like 

 muscles, are capable of being awakened to 

 activity by nerves, and become the seat of 

 chemical changes, accompanied with the 

 liberation of heat and the giving off of 

 materials differing from those found in the 

 blood. 



Not less important were Ludwig 's inves- 

 tigations of the interchange of oxygen and 

 carbon dioxide gas between the blood and 

 the tissues, and the blood and the air in 

 the lungs. The blood-gas-pump devised by 

 Ludwig and Setchenow in 1859, a new ap- 

 plication of the Torricelli vacuum, proved 

 the key to unlock many difficult problems. 

 There followed many investigations by his 

 pupils Schoffer, Holmgren, Preyer, Alex- 

 ander Schmidt, giving the first measure- 

 ments of the tension of the gases of the 

 blood, and by Worm-Muller and Donders 

 on the conditions which determine the ten- 

 sion. 



Ludwig opened up still another line of 



work, the chemical changes occurring within 

 special organs, when he found that it was 

 possible to separate organs from the gen- 

 eral circulation, and to study their metab- 

 olism by keeping them alive by artificially 

 circulating defibrinated blood . through 

 them ; e. g., the heart of the frog was thus 

 kept alive and acting for many days, and 

 the effect of temperature, foods and drugs 

 upon its activity were examined. 



His studies into the formation of lymph, 

 and the cause of its movement in the lym- 

 phatics, were of great value. According to 

 Ludwig the plasma of the blood filters 

 through the walls of the blood vessels, and 

 so food materials are supplied to the vari- 

 ous tissues. It is also the pressure of the 

 blood which is the principal cause of the 

 movement of the lymph stream. Where 

 this is not sufficient, as in the case of the 

 large cavities of the body, there are special 

 pumping arrangements provided: in the 

 abdomen and in the pleural cavities it is 

 the respiratory movements of the diaphragm 

 and of the chest walls which are respon- 

 sible for the flow. 



The conditions which determine the cir- 

 culation of the blood always aroused his 

 keenest interest, and it was because of his 

 desire to grasp their significance that he 

 was led to what has proved the most fruit- 

 ful of his discoveries, the graphic method 

 of recording physiological movements. In 

 1846, while still- in Marburg, he studied the 

 relation which exists between the move- 

 ments of respiration and the pressure of the 

 blood. He connected a U-shaped manom- 

 eter tube partly filled with mercury, with 

 an artery, but the movements of the column 

 of mercury were so rapid and complex 

 that the eye failed to retain them. It was 

 then that he conceived the idea of recording 

 the cha'nges in pressure, and devised the 

 kymographion. Let me quote his own 

 words in his paper, "Beitragen zur Kent- 



