BLOOD-SERUM. 



129 



Before using the apparatus the extremity of the first 

 tube is heated in the gas-flame, and by touching this 

 point with a piece of pointed glass rod it is gently drawn 



FIG. 21. 



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 /', 

 blood-serum collected in bottom of second tube. 



out into a fine cannula. When the animal has been pre- 

 pared for the operation and a vessel exposed, the point 



9 



