488 



CIRCULATION OF BLOOD AND LYMPH. 



in terms of a column of blood or water. For continuous obser- 

 vations and permanent records the height of the column of mer- 

 cury and its variations during an experiment are recorded by the 

 device represented in Fig. 192. 



Fig. 192. — A, Schema to show the recording mercury manometer and its connection 

 with the artery: M, The manometer with the position of the mercury represented in black 

 (the pressure is given by the distance in millimeters between the levels 1 and 2 ; one-half of 

 this distance is recorded on the kymographion by the pen, P) ; F, the float resting upon the 

 surface of the mercury; G, the cap through which the stem carrying the pen moves; E, offset 

 for driving air out of the manometer and for filling or washing out the tube to the artery ; 

 R, the receptacle containing the solution of sodium carbonate ; c. the cannula for insertion 

 into the artery; w, the washout arrangement shown in detail in B. 



B, The washout cannula : c, the glass cannula inserted into the artery ; r, the stem 

 connected with the reservoir of carbonate solution; o, the stem connected with the manom- 

 eter. The arrows show the current of carbonate solution during the process of washing 

 out, the artery at that time being closed by a clamp. 



The blood-pressure record (Fig. 193) shows usually large rhyth- 

 mical variations corresponding to the respiratory movements and in 

 addition smaller waves caused by the heart beat. The causes of the 

 respiratory waves of pressure are discussed in the section on respi- 

 ration. Regarding the heart waves or pulse waves the usual record 

 obtained by means of a mercury manometer gives an entirely false 

 picture of the extent of the variations in pressure caused by the heart 

 beat. The mass of mercury possesses considerable weight and iner- 

 tia, which unfits it for following accurately very rapid changes in 

 pressure. When the pressure changes are slow, as in the case of 

 the long respiratory waves seen in the record, the manometer un- 



