i6 ARE THE EFFECTS OF USE INHERITED? 



The lateness and irregularity of the wisdom teeth 

 are sometimes supposed to indicate their gradual 

 disappearance through want of room in a diminish- 

 ing jaw. But a note on Tasmanian skulls in the 

 Catalogue of the College of Surgeons (p. 199) shows 

 that this lateness and irregularity have been com- 

 mon among Tasmanians as well as among civilized 

 races, so that the change can hardly be attributed 

 to the effects of disuse under civilization. 



small quantities. But the submaxillary and sub-lingual saliva 

 poured out at the foot of the lower incisors and held in the front 

 part of the jaw as in a spoon, " differs from parotid saliva in being 

 more alkaline " (Foster's Text Book of Physiology, p. 238 ; Tomes, 

 pp. 284, 685). One observer says that the reaction near the lower 

 incisors is " never acid." Hence (I conclude) the remarkable im- 

 munity of the lower incisors and canines from decay, an immunity 

 which extends backwards in a lessening degree to the first and 

 second bicuspids. The close packing of the lower incisors may 

 assist by preventing the retention of decaying fragments of food. 

 Sexual selection may promote caries by favouring white teeth, which 

 are more prone to decay than yellow ones. Acid vitiation of the 

 mucus might account both for caries and (possibly) for the strange 

 infertility of some inferior races under civilization. 



