ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 25 



with the tendency to form tnmonrs is the prodnction of pigmented spots 

 or patches on the skin, of a cafe-an-lait colonr. The disease may occnr 

 without a break for several generations, and is equally apt to come down 

 the male and the female line. Consequently, it looks as though the 

 hereditary factor is a dominant one. In each affected fraternity about 

 50 p.c. of the individuals are affected. The fact that neurofibromata 

 have an inheritable basis strengthens the view that cancers in genera 1 

 have such a basis. J. A. T, 



Heredity of Susceptibility to a Transplantable Sarcoma. — C. C. 

 Little {Science, 1920, 51, 467-8). From experiments with Japanese 

 waltzing mice it is concluded provisionally (1) that there is hereditary 

 susceptibility to the growth of a transplanted sarcoma, to which common 

 mice are not susceptible : (2) that from three to five factors, probably four, 

 are involved in determining the susceptibility ; (3) that for susceptibility 

 the simultaneous presence of these factors is necessary ; (4) that none 

 of these factors is carried in the sex (X) chromosome ; and (5) that 

 these factors Mendelize independently of one another. J. A. T . 



Inheritance of Tremor.— E. Bergman {Hereditas, 1920, 1, 98-l<)6). 

 Hereditary tremor consists in small, rapid, involuntary, and rhythmic 

 contractions of certain groups of muscles, especially in -the hands and 

 arms. It is usually present without intermission except during sleep 

 and perfect rest. It is usually increased by motion and exercise. The 

 tremor may be rather rapid (eight to ten vibrations a second) or com- 

 paratively slow (three to four vibrations a second). A case is discussed 

 where the tremor occurred in four members of a family in three genera- 

 tions, and apparently behaved as a dominant. J. A. T. 



Inheritance of Genotypical Deaf-mutism. — H. Lundborg {Herc- 

 cUtas, 19:^0, 1, ;!5-4o). Deaf -mutism may be acquired or innate. 

 Acquired deaf-mutism may originate in utero or after birth. Con- 

 sequently " congenital deafness " is not always heritable. In the past 

 there has not been sufficient care taken to discriminate between geno- 

 typical, or innate, and phenotypical, or acquired, deaf-mutism. Trying to 

 make this discriminatian, Lundborg has arrived at the conclusion that 

 there is constitutional or genotypical deaf-mutism, and that it behaves as 

 a recessive and monohybrid character. He criticizes and rejects Plate's 

 theory that deaf -mutism is a dihybrid character, requiring two factors to 

 bring it about. Lundborg pleads, however, for an extension of precise 

 enquiry in regard to this important case. J. A. T. 



Polydactyl Negro Twins.— C. H. Danforth {Amer. Journ. Phijs. 

 Anthropol, 1919, 2, 147-65). A comparison of the left hands of 

 polydactyl negro twin infants (possibly uniovular in origin) with the 

 left hand of a normal white infant for reference. In several respects 

 the three infants showed like departures from what is generally con- 

 sidered as the normal adult condition. The extra digits were found to 

 present the elements of a normal finger in a shortened and more or less 

 abortive condition. The twins exhibited a marked similarity in respect 



