PARABIOSIS 



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Parabiosis. Not only may an organ or a portion of tissue from 

 one individual be engrafted on another, but two individuals may be 

 so united that a greater or smaller degree of physiological in- 

 timacy is produced between them. Occasionally, as in the famous 

 Siamese twins, an anomaly of development results in such close 

 anatomical union of the circulatory and other systems that in 

 certain respects the two individuals constitute almost a single 

 organism, and cannot be separated by surgical interference. A 

 less intimate union can be established experimentally by opening 

 the peritoneal cavities of the two animals, and suturing the skin 

 and connective tissue together so as to permit of permanent 

 communication. Pairs of animals living in this condition (so- 

 called parabiosis) have been utilized for the study of certain 

 questions in immunity. White rats have been kept alive in para- 

 biosis for as long as thirty- four days in order to test the question 

 whether destructive antibodies for cancer are present in the circula- 

 tion (Rous), since it has been shown that circulating antibodies easily 

 pass from one to the other of such a pair of animals (Ehrlich.) 

 One of each pair of rats had a growing tumour produced by 

 transplantation, while the 

 other had been proved resis- 

 tant 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 Fig. 466. Contractions of Rabbit's Uterus 

 ligament and vagina, support Ring. At 41 Ringer's solution was re- 

 the horns of the uterus on soft placed by adrenalin solution, i : 1,000,000. 

 threads. Ligature the vagina Time trace, half-minutes, 

 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. 198), kept at body 

 temperature (38 C.) in a small beaker immersed in a water-bath, as in 

 the experiment on the contraction of isolated intestine (p. 446). *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 



