REPRODUCTION 



1025 



animals living in this condition (so-called parabiosis) have bseii 

 utilized for the study of certain questions in immunity. White rats 

 have been kept alive in parabiosis for as long as thirty-four days in 

 order to test the question whether destructive antibodies for cancer 

 are present in the circulation (Rous), since it has been shown that 

 circulating antibodies easily pass from one to the other of such a 



FIG. 448. SUTURING BLOODVESSELS. METHOD OF APPROXIMATING EDGES AND 

 PUTTING IN CONTINUOUS SUTURE (AFTER GUTHRIE). 



The needles are'very fine cambric sewing-needles, and the threads single strands 

 of Chinese twist silk or human hair. Needles and threads are sterilized in 

 paraffin-oil. (Method of Carrel and Guthrie.) 



pair of animals (Ehrlich). One of each pair of rats had a growing 

 tumour produced by transplantation, while the other had been 

 proved resistant to the same type of tumour. No evidence of the 

 passage of an antibody was found in this case. 



PRACTICAL EXERCISE. 



Contractions of Isolated Uterine Rings. Kill a female adult 

 rabbit by striking it at the back of the neck. A rabbit which is 

 not pregnant, or only at the beginning of pregnancy, should be 

 selected. Open the abdomen, and carefully remove the uterus. 

 While separating the organ from the broad ligament and vagina, 

 support the horns of the uterus on soft threads. Ligature the 

 vagina before cutting through it, and cut below the ligature, which 

 can then be used to manipulate the uterus. Do not pinch the uterus 

 with forceps, and handle it as little as possible. At once place it in 

 Ringer's solution (p. 186), kept at body temperature (38 C.) in a small 

 beaker immersed in a water-bath. Cut a ring of tissue about 

 i centimetres in width from one of the horns. Tie a loop with a 

 fine silk thread at each end of a diameter of the ring, pinching up a 

 little of the external coat to do so with fine forceps. Make the 

 arrangements necessary for recording contractions of the ring while it 

 is immersed in a very small beaker or a glass cylinder in the bath, as 

 in Experiment 12, p. 185, but do not divide the ring. A narrow 

 glass tube connected by a rubber tube with a cylinder of oxygen 

 must be arranged to dip down to near the bottom of the beaker. 

 The valve of the cylinder is turned cautiously, so as to permit oxygen 

 to bubble slowly through the solution. After a longer or shorter 

 interval spontaneous rhythmical contractions of the uterus ring 



65 



