Ill 



example, as tlie stream-gauge, for recording the flow in a blood- 

 vessel, or the methods used by him for maintaining artificial circula- 

 tion in a separated part or organ, so as to observe its function inde- 

 pendent of the organism to which it has belonged ; all of which have 

 yielded information of fundamental importance. 



Another instrument invented by Ludwig, the value of which to 

 physiology has been nearly as great as that of the kymograph, is the 

 mercurial blood-pump, the purpose of which is to separate from a 

 known quantity of blood derived directly from the circulation, the 

 mixture of gases which it yields to the vacuum. It is sometimes 

 stated that Ludwig derived this instrument from Professor Lothar 

 Meyer, who Avas, at the time he entered on his investigation of the 

 gases of blood, engaged in researches on the same subject in Bun sen's 

 laboratory, and employed an apparatus for the extraction of the blood 

 gases in which the vacuum was produced by the condensation of steam. 

 To Meyer* belongs the credit of having first succeeded (1857) in ex- 

 tracting the blood gases, and of having made the first reliable analyses 

 of them ; but it was Ludwigf who, in 1859, invented the first mercurial 

 pump, and described it in a paper published under the name of his 

 pupil Setschenow. After that time the pump underwent various 

 modifications of form but not of principle, in the progress of the 

 extended series of researches on the gases of the blood which Ludwig 

 commenced at Vienna, and carried out at Leipzig ; so that the final 

 form — that employed in the Leipzig laboratory by A. Schmidt in his 

 research on the carbon dioxide of the coloured blood corpuscles and 

 usually described as Ludwig's — although the same in principle, differs 

 considerably in aspect from the original one. 



The importance of the discovery of an exact method of investi- 

 gating the gases of the blood could be best judged of if it were 

 possible to submit to the reader a summary of the researches con- 

 ducted by means of it during the last thirty-five years. Of the 

 enormous amount of work which has thus been done, Ludwig and his 

 pupils have contributed a very large proportion. Of the earlier 

 experiments carried out in the Vienna laboratory, Ludwig himself 

 published a general account in 1865. After his removal to Leipzig, 

 the subject developed in so many directions, that it is impossible to do 

 more than mention certain series of observations such as those on 

 the gases of lymph, on the gaseous exchange of: living muscle, on 

 the presence of oxidisable material in the blood and its significance, 

 <fcc. These and other researches relating to the physiology of the 

 respiratory exchange, which were conducted under Ludwig's direction, 



* Meyer, " Die Gl-ase des Blutes," ' Zeitsch. f . rat. Med.,' ]S T .F., vol. 8, p. 277. 

 1857. 



f Setschenow, !< Beitriige zur Pnemnatologie des Blutes." ' Wiener Ber./ toI. 

 36, p. 304, 1859. 



b 2 



