LXIL] 



RIGID AND ELASTIC TUBES. 



299 



(a.) To represent the heart or the weight of a column ot fluid arrange 

 a Marriotte's flask or funnel on a stand, and to the outflow tube attach a 

 narrow india-rubber tube, and clamp it after filling it with normal saline 

 (to represent defibrinated blood). Fill one bulb of the instrument with 

 defibrinated blood, the other with almond oil, and close the top of the 

 instrument with a glass plug. 



(b. ) Suppose the tube to represent an exposed 

 artery ; about the middle of the tube apply two 

 ligatures about an inch apart (or two clamps). 

 Divide the part of the tube included between the 

 two ligatures, and tie into either end the nozzles 

 provided with the instrument. Call the one 

 next the reservoir or heart h, and the other on 3 

 k. Fix the instrument into the nozzles, the 

 bulb A being filled with oil and in connection 

 with h, B with defibrinated blood and connected 

 with k. The instrument is fixed in position by a 

 support provided with it, while a handle which 

 fits into two tube-sockets on the upper surface of 

 the disc (e, e^) is used to rotate the one disc on 

 the other. 



(c.) All being now ready, take the clamp off 

 the reservoir of blood and the clamps or ligatures 

 off the artery. The defibrinated blood flows into 

 the bulb A, displaces the oil in it towards B, 

 the detibrinated blood of B being forced out into 

 the artery and caught in a suitable vessel. Of 

 course, in the animal this blood simply passes 

 into the artery. As soon as the bulb A is filled 

 with blood, which is indicated by a mark on 

 the glass, the disc is suddenly rotated by the 

 hand, whereby B communicates with h, and A 

 with k. The blood now flows into B, displacing 

 the oil in it into A, and as soon as this takes 

 place, the disc is again rotated. This process is 

 repeated several times. Count the number. The 

 bulbs have the same capacity and are exactly 



calibrated. 



The time is most conveniently measured by 



connecting the rheometer with an electro-magnet 



registering on a drum each rotation of the disc, 



and under this a time-marker records seconds. 

 Example. Suppose each bulb holds 5 cc., and 



suppose the bulbs to be filled ten times with 



blood during 100 seconds, i.e., 50 ccm. flowed 



from the tube in I second. Suppose the diameter 



of the tube to be 2 mm. (i.e., radius = I mm.), 



this would give a sectional area of 3. 14 mm. 

 The velocity (V) is calculated by the ratio of 



the quantity discharged (Q) to the sectional area (S), i.e., the quantity of fluid 



flowing across any section in unit of time -r area of that section. Hence 



.Q 



FIG. 222. Rheometer. 



V = 



S 



.5 cc., or what is the same thing, 500 cmm., are discharged in one second ; 

 therefore 'the velocity is = ' = 159 mm., or about six inches per second. 



