191 1 ] A. J. ROSANOFF AND FLORENCE I. ORR 235 



spectively, lesser and more pronounced degrees of recessiveness, 

 a given neuropathic condition may accordingly be represented 

 either by the symbol RR or Rr ; and similarly the condition of a 

 normal subject who represents simplex inheritance, i. e., who 

 inherits the neuropathic taint from one parent, may be repre- 

 sented either by the symbol DR or Dr. It may be readily seen, 

 then, that in the case of either the first or second combination 

 there are possibilities of offspring with more than one type of 

 neuropathic defect, i. e., of defects of different degrees of reces- 

 siveness, as may be shown by the following formulae: 



1. RrxRrooRR + 2Rr + rr. 

 Rr X rr 00 Rr -I- rr. 



2. RrxDrooDR-f-Dr-f Rr + rr. 



The neuropathic conditions in the children resulting from such 

 matings would not necessarily be equivalents. 



But in the case of the fourth type of mating, that of two sim- 

 plex individuals, /. e., two individuals who are normal but carry 

 the taint from their ancestors, the neuropathic offspring which 

 may result would in any instance show defects which are theoret- 

 ical equivalents ; for from every theoretically possible variety of 

 combination only one type of neuropathic offspring can result, 

 as may be shown by the following formulae : 

 DR X DR CO DD + 2DR -f- RR. 

 DRxDrooDD + DR + Dr + Rr. 

 Dr X Dr 00 DD -f- 2Dr + rr. 

 Clinical manifestations will, of course, vary with the personal- 

 ity of the subject, the age at which the disorder makes its appear- 

 ance, the nature of the exciting cause, and other environmental 

 conditions ; but in spite of such variations we are able, in the 

 light of a better knowledge of the mechanism of heredity, to 

 identify neuropathic equivalents at least when they occur in 

 brothers and sisters who are the offspring of the matings of the 

 fourth type. 



In matings of this type only one-fourth of all the offspring, on 

 the average, exhibit the neuropathic condition; therefore most 

 such families have not more than one neuropathic subject and 

 do not afford an opportunity of comparing neuropathic equiva- 

 lents ; but many large families, or some in which by an unlucky 

 chance more than one neuropathic subject has resulted, do afford 



