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phatic system may become supplemented by the thymus. In ado- 

 lescence, when the building is completed, the supplementary gland 

 retires. This could also explain why the extirpation of the thymus 

 causes no trouble, even if its function is important — because the 

 rest of the lymphatic system takes over. There are many examples 

 of such compensation. So our logic may have holes and it may just 

 as well be (for all we know) that the whole lymphatic system is 

 one big gland of internal secretion, may be even the biggest and 

 most important of all, a possibility which has hitherto been over- 

 looked only because it is too obvious. 



These assumptions might also explain why thymus extirpation 

 benefits only part of the myasthenic patients. If myasthenia is due 

 to the dysfunction of lymphatic tissue, then the success of the 

 thymus extirpation has to depend on the question how far this 

 dysfunction was localized to the thymus. 



Myasthenia is characterized by a great fatigability of muscles. I 

 was often impressed by the great fatigability of infants. I would 

 almost say that all infants are myasthenics. An adult dog will out- 

 run almost any other animal, but a three-year-old child (which has 

 nearly the same amount of muscle for body weight) tires in a short 

 walk and is unable to lift a heavy weight. Nature may have seen to 

 it that while the building process is going on, it should proceed 

 undisturbed by exaggerated function. Nature often kills more than 

 one bird with the same stone and it is possible that the same sub- 

 stance which is involved in the building process might also keep 

 the muscles at a low functional level. 



The tentative assumption that the thymus (and, possibly, other 

 parts of the lymphatic system) produces some substance involved 

 in protein synthesis finds some support in the observations of 

 Gudernatsch which, a few decades, ago, focused attention for a 

 short while on the thymus. Gudernatsch found that tadpoles, fed 

 on thymus glands, showed a retarded metamorphosis with an in- 

 creased growth, developing into giant tadpoles. Attempts to isolate 

 the active substance responsible for this effect failed and the in- 



