140 PHYSIOLOGY 



right itself when turned over on the back and sometimes suc- 

 ceeds. Later ages showed gradual improvement in equilibration 

 with increasing powers of coordination. 



Structural conditions. Fetus 35 mm. Semi-circular canals 

 well formed and ampullae innervated. Cristae acusticae have 

 sensory and supporting cells well differentiated. Central con- 

 nections of the vestibular nerve well defined. The same condi- 

 tions at birth. At later ages muscle tonus the use of the 

 vibrissae and sight, all aid in equilibration. 



Smell : Reactions. Age, one day. Apparent responses to 

 olfactory stimuli were obtained at this age reaction time long. 



Later stages : olfactory sense gradually improves from day 

 to day. 



Structural conditions. At one day, olfactory area contains a few 

 differentiated sensory cells. 



Later stages : a gradual perfecting of the olfactory apparatus 

 in general. 



Taste : Reactions. First day after birth, sense of taste un- 

 certain. All substances appear to be disagreeable. 



Later stages : Sense of taste slowly developed. 



Structural conditions. First day after birth taste buds not 

 demonstrated. Dome shaped papillae are present on the anterior 

 part of the tongue. 



Later stages : by the ninth day taste buds on the sides of the 

 circumvallate papillae are found, and a decidedly different 

 organ in the dome shaped papillae. 



Hearing : Reactions. No reactions to sound before the 12th 

 day after birth. From that age on there is a gradual but rapid 

 increase in the ability to hear. 



Structural conditions. By the 12th or 13th day the organ of 

 Corti is differentiated in part and the cellular plug in the external 

 auditory meatus, which was intact for the first eleven or twelve 

 days, is undergoing liquefaction and has become imperfect. The 

 next few days witness the complete differentiation of the organ 

 of hearing. 



Sight : Reactions. No response to light was obtained before 

 the opening of the eyes on the sixteenth or seventeenth days. 



