MEASUREMENTS 



321 



rubbing lightly on a level surface of smoked paper moving hori- 

 zontally. At the same time, the volume of each respiration can 

 be found. 



The respiratory curves can also be registered by the pneumo- 

 graph. This apparatus must be fixed to the subject so that it 

 is not shaken by his work and exploratory tambours can be 

 placed on the workman's back instead of on his chest. After 

 having obtained the registration when in repose, leave the pneumo- 

 graph in place for a registration when working, and the traces 

 may then be strictly comparable. 



248. Circulatory Activity. The rhythm of the beat of the heart 

 and the pulse can be registered by the cardiograph and the trans- 

 mitting sphygmograph ( 195). It is difficult to place the various 

 apparatus in precisely the same position for each experiment 

 so that the curves obtained may be strictly comparable. 



It is best to determine the arterial pressure before and after 

 work, using, for instance, Faction's oscillometer (fig. 228). This 

 consists of a rubber tube B covered with fabric placed round 

 the wrist and connected by a rubber tube a to the oscillometer. 

 The latter consists of a vessel E, in which air is compressed by 

 means of a pump, P, to a pressure always higher than that which 

 is to be measured, 20 centimetres, for instance, which is read 

 on the gauge M. The passage fb a being open, there will be the 

 same pressure in the wrist tube B as in the aneroid box c, and the 

 needle, /, attached to the metal diaphragm, will be stationary. 

 Lower the pressure of the air a little by unscrewing the valve V, 

 and at intervals tighten the contact S to close the passage. As 

 soon as the pressure of air has attained that of the blood, the 

 needle will be ready to oscillate. The beginning of that oscillation 

 marks the systolic pressure, the strongest pressure of the artery. 



Again decrease the pressure of the air and the oscillations will 

 indicate the diastolic pres- 

 sure. These pressures are 

 read on the gauge M. 



249, Measurement of 

 Tactile Sensibility : The 

 Esthesiometer. If the skin 

 is touched with a metal 

 point, it is possible, with 

 closed eyes, to indicate with 

 greater or less accuracy the 

 spot touched. This is what 

 Weber called the sense of 

 place or capacity of localisa- 

 tion . f 1 ) This capacity can be 

 measured by two methods : 



FIG. 228. 



Pachon's sphygmometric oscillometer. 



Weber Wagner's Handbuch d. Physiol., iii., 2 Abt.. p. 524. 



