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THE AMERICAN NATURALIST [Vol. LIV 



in itself was perhaps the cause of the disease. All mod- 

 ern studies on inbreeding, however, seem to strengthen 

 the conclusion that while inbreeding may, by the "concen- 

 tration" or production of unfavorable character com- 

 binations, and particularly by the loss of important phys- 

 iological factors which are necessary to the well being of 

 the individual, result in lowered vitality and in the ap- 

 pearance of various defects, it is nevertheless a means 

 rather than a cause of bringing these into expression. 



Further evidence that the palsy was not produced by 

 the inbreeding as such is furnished by the fact that the 

 lines in which it appeared were no more inbred than many 

 other lines that have been carried on in the laboratory in 

 connection with other problems, but in which no tendency 

 to such a defect has manifested itself. Our whole stock, 

 in fact, of some 2,200 litters and over 5,000 offspring has 

 all descended from not more than 50 original animals, 

 and as has already been stated, there is reason to believe 

 that some of these were related. In order to show the 

 intensity of the inbreeding in some cases, it may be men- 

 tioned that in one experiment a male was bred back to 

 his daughters for four successive generations, and with 

 no apparent ill effects. Inbreeding as a predisposing 

 cause may therefore be ruled out. 



4. The spasms which form the characteristic reaction 

 of the palsied animals are clearly due to lack of nervous 

 control, especially when voluntary movements of the legs 

 are attempted, and under excitement. It may therefore 

 be that there is some heritable defect of the central nerv- 

 ous system. Examinations which have been made for us 

 by Dr. C. H. Bunting have, however, shown no lesions of 

 the nervous system to which these effects could be at- 

 tributed. 



5. Disturbances of some of the glands which supply 

 internal secretions are known to produce nervous irri- 

 tability and conditions of spasm and tetany. Partic- 

 ularly is this true of the parathyroid, and some of the 

 symptoms accompanying disturbances of this gland re- 

 semble to a certain extent, at least superficially, the con- 



