BLOOD-SERUM 



123 



formed by drawing out the tube while heated. The second 

 tube also has a similar constriction about 20 cm. from its 

 mouth. 



FIG. 20 



u 



Rivas apparatus for collecting blood-serum: A, long narrow neck on 

 first tube; B, constriction on tubes near mouth; C, invaginations on first 

 tube; D, small cannula drawn out on extremity of first tube; E, blood- 

 clot, and F, blood-serum collected in bottom of second tube. 



The two tubes are now fitted together by inserting the 

 one with the long narrow neck into the second tube; a small 



