378 INFLUENCE OF CONTRACTING MUSCLE ON THE BLOOD. [BOOK I. 



into which the venous blood may flow, and where it may be collected 

 for analysis. 



It is convenient and advisable to take the blood which is needed in 

 the experiment, from the dog whose muscles are examined. The dog 

 should be .first bled nearly to death, and its blood then defibrinated 

 and made ready for the experiment. 



Various conditions of blood must be used for comparison ; 

 arterialized blood, or blood perfectly reduced, or asphyxiated blood, 

 or asphyxiated blood restored by oxygen 1 . 



After its blood has been prepared, the dog should be killed and its 

 muscles separated in the manner already described. They are then to 

 be transferred to a glass vessel, T, T, such as is figured in Fig. 59, and 

 covered over by a glass plate. It will be observed that the vessel is 

 perforated so as to allow the tubes conveying arterial and venous blood, 

 A, V, to pass into and out of it, and to permit the passage of wires, E, E, 

 connecting the muscles with an induction coil by which tetanus may be 

 induced. If it is thought necessary, the muscles may be attached to 

 a lever so arranged as to record its movements upon a revolving 

 cylinder. The blood may be forced into the arteries by means 

 of a column of mercury, M, the pressure of which admits of careful 

 regulation. 



It will be found necessary to increase the pressure of mercury in 

 the course of an experiment in order to maintain a constant flow of 

 blood. The pressure of mercury (40 60 mm.) which, at the beginning 

 of an experiment, serves to drive 2 - 5 to 3 c.cm. of blood per minute 

 through a biceps muscle of 150 200 grms. weight, will have to be 

 more than doubled (100 150 mm.) after four hours in order to do the 

 same amount of work. It must not be supposed that the resistance 

 to flbw suffers a regular increase during this time ; on the contrary, the 

 gradual increase is interrupted by frequent variations to and fro, 

 for which there is no assignable cause. The observer must pay 

 unremitting attention to the rate of outflow, if he wishes to maintain 

 it constant even for a few minutes 2 . 



The cause of these variations in the rate of outflow is left obscure by 

 Ludwig and Schmidt ; but it is extremely probable that part of the obstruc- 

 tion is due to the gradual death and contraction of the smaller arteries. 

 When the driving pressure is raised, the constricted vessels will again be 

 opened for the passage of blood, and the original rate of flow will be restored. 

 If this cause of obstruction is admitted, it follows that the more rapid out- 

 flow of blood from a muscle which is brought about by raising the driving 

 pressure, may be due not so much to accelerating the current of blood, as to 

 enlarging the number of channels for it. In other words, raising the pressure 

 of injection does not bring a larger volume of blood to play upon the same 

 amount of muscular tissue, but rather brings more muscle under the influence 

 of the blood 3 . 



1 Ludwig and Schmidt used small pieces of iron wire to effect the reduction. 



2 Ludwig and A. Schmidt, Op. cit. p. 27. 



3 Pfliiger, " Ueber die physiologische Verbrennung in den lebendigen Organisinen.' 

 rfliiger s Arch. Vol. x. 1875, p. 350. 



