MECHANICS OF THE CIRCULATION IN THE VESSELS 123 



of small calories (gramme-calories) given off in m minutes, T the tem- 

 perature of the blood entering the hand, T 1 the temperature of the 

 blood leaving the hand, and s the specific heat of blood (0-9). For 

 purposes of comparison the volume of the hands is measured, and the 

 blood-flow expressed in grammes per 100 c.c. of hand per minute. 

 Further details are given in the Practical Exercises (p. 218). Fig. 51 

 shows one of the calorimeters on its adjustable stand. The collar of 

 thick felt which fits closely around the wrist, and prevents loss of heat 

 from the orifice through which the hand is 

 inserted, is shown standing on the top of 

 the calorimeter, as also the thermometer 

 with the small sliding lens, or ' reader.' In 

 Fig. 1 08, p. 219, the position of the subject 

 with hands in the calorimeters is shown. 



*/* 



Fig. 50. Cybulski's Arrangement for recording 

 Variations in the Velocity of the Blood. A, tube 

 connected with central, B with peripheral, end 

 of divided bloodvessel. The blood stands higher 

 in the tube C than in D. A beam of light passing 

 through the meniscus in both tubes is focussed by 

 the lens L on the travelling photographic plate E. 

 The velocity at any moment is deduced from the 

 height of the meniscus in the two tubes C and D. 



Fig. 51. Calorimeter with 

 stand for measuring 

 blood-flow in hand. 



Of these methods, 3 and 4 are alone suited for the study of the 

 velocity-pulse, that is, the change of velocity occurring with every 

 beat of the heart. The curves obtanied by Chauveau's dromo- 

 graph show a general agreement with blood-pressure tracings taken 

 by a spring manometer, and with records of the external pulse 

 obtained by a sphygmograph. There is a primary increase of 

 velocity corresponding with the ventricular systole, and a secondary 

 increase corresponding with the dicrotic wave (Fig. 54). Like all 

 the other pulsatory phenomena, the velocity-pulse disappears in the 

 capillaries, and is only present under exceptional circumstances in 

 the veins. 



