DISCUSSION 327 



ranting I think is no longer mysterious, although it might still yield 

 surprises. 



Billinghatn: After three years' hard work in collaboration with a 

 pathologist, we have learned a lot of things about runt disease in the rat 

 but we still don't know what kills them. 



Nakic: I have had no experience with runt disease, but I have had 

 with parabiotic disease which is just another form of graft-versus-host 

 reaction. We have observed two forms of the disease: the "white" and 

 the "red" form, the difference being that in the wliite form the pre- 

 dominant symptom is anaemia while in the other it is absent. In the 

 white form one can be quite sure that the immediate cause of death is 

 profound anaemia, which may develop in a matter of hours, the number 

 of erythrocytes dropping from about 10 milhon to less than 2 million. 

 I am not sure about the cause of death in the red form. One observes 

 wasting, diarrhoea, focal necroses in the liver, and atrophy of the 

 lymph organs. We haven't observed any overt infections, but never- 

 theless it may be an infection which finishes off the animal. 



Russell: What is red in the red form? 



Nakic: In parabiotic disease there is paralysis of the capillaries every- 

 where in the body, even in the animals suffering from anaemia. There- 

 fore the non-anaemic animals appear very red because of the dilated 

 capillaries wliile the grafts look pale by comparison although they are 

 normally coloured. 



Miller: What is the histological appearance of the thymus and the 

 thyroid in animals suffering from runt disease ? 



Voisin: I don't know about the thymus in my animals. Dr. Billing- 

 ham has done some work on this subject. 



Billinghatn: In acute runt disease in the rat, there is complete atrophy 

 of the thymus. Only a few strands of fibrous connective tissue can be 

 located in the site normally occupied by this organ, and two nodes 

 which are normally concealed by the thymus are very conspicuous in 

 runts as a consequence of hypertrophy. 



Krohn: This is typical of acute adrenal hyperactivity, which would 

 go with the cause of death but probably not itself be the cause of death. 



