Page:The Scientific Monthly vol. 3.djvu/204

 198 TEE SCIENTIFIC MOJfTHLY

It further appears that certain histories of human families are stri- king enough^ even with present imperfect methods of obtaining data^ to indicate strongly the presence of hereditary tendencies to cancer in man. Not only is this the case^ but the problem may be approached from the opposite viewpoint and the data supposed to show the non-inheritable nature of human cancer may be examined. Such work as that of Pear- son, and other biometricians, while adding little in accuracy to the meth- ods of obtaining data on human inheritance, are guilty of a gross mistake in their method of analysis. Their weakness lies in the fact that they are able to detect only the direct or Oaltonian type of inheritance and are utterly unable to recognize or utiUze the well-defined and accepted principles of transmission by individuals of hereditary potentialities throughout an indefinite number of generations without any morpho- logical manifestation of those potentialities until similar or otherwise suitable mates appear. BiometricaJ methods are of undoubted value, but they fall short of the whole truth, and can not in this case be taken as alone disproving the occurrence of hereditary factors in the case of human cancer.

An example of an actual case of inheritance in mice may serve to make clear the limitations of biometric methods of detecting even the fact of inheritance. All pigmented mice are classifiable into two groups, those having solid colored or *' self " coats, and those having white spots of varying sizes. In other words, the mouse is either '^eelf or ^' spotted '' in appearance. Supposing a mixed population of let us say 15,000 mice, some of which are " self,*' some " spotted,*' and let us try to prove that spotting is or is not inherited. Following certain biometric methods we shall consider the parents and grandparents of each spotted mouse as compared with the same ancestral generations of non-spotted (^'self") mice.

Any of the following types of ancestry are possible and have actually been repeatedly obtained in the laboratory.

Mftting Mouae Obterred Parenti

Belf. (a) Self.

��Self.

���/Spotted (Spotted

(M Self J 11^^^^

rseif J?*"

<*> «P*»"«^ <^^ Iself

7Self

�� �