MAMMALIA— PHYSIOLOGY 



477 



429.) There are four types of taste: Sweet, sour, salt and bitter. 



In eating one receives sensations from taste, smell, cutaneous sense 



and temperature sense. The child prefers sweets while sour and 



bitter are unpleasant. Children have more taste organs than the 



adults since some of the taste buds atrophy as age advances. One 



section of the tongue is wholly insensitive to taste. The anterior 



portion of the tongue is sensitive to sweet substances, the lateral 



portions are sensitive to sour and salt, while 



the posterior portion is extremely sensitive to 



bitter substances. 



Kinaesthetic Sense. — Certain kin aesthetic 



sense organs are contained in the skeletal 



muscles, tendons and joints and transmit to 



the brain knowledge of positions of parts of 



the body. 



Organic Sensations. — Many subconscious 



sensations concerned with visceral activities 



are carried to the brain by the aid of organs 



connected with the digestive, respiratory and 



circulatory systems. Unusual stimuli may 



produce thirst, hunger, nausea or suffocation. 

 Weight of the Brain. — The brain of the 



average adult human female weighs 44.5 



ounces and that of the male 49.75 ounces. 

 Cases have been recorded in which the brain 



attained a weight of 74.8 ounces, one case 



being that of an idiot. The weight of the 



brain of the gorilla is 15 ounces. In the 



healthy body the relation of the weight of tesy of Henry Holt & Co.) 



the human brain to that of the body is 1-41. 



Transmission of an Impulse. — From a sense organ in the skin an 

 impulse passes to the sensory fiber of a spinal nerve, in at the dorsal 

 (posterior) root to the dorsal horn of the cord and to a spinal sensory 

 cell. Thence it goes up the dorsal column to the sensory cell of the 

 optic thalamus. From the optic thalamus it passes to the sensory 

 cell of the cortex in the localized area indicated by its original source. 

 Then the impulse to act, beginning at the motor cell of the cortex, 

 passes across to the motor cell of the corpus striatum (see Figure 

 256), thence down the anterior ventral colujnn of the spinal cord to 

 a spinal motor cell in the ventral horn, out at the ventral root of the 



Fig. 255. Upper sur- 

 face of the tongue. /, 

 circumvallate papillae; 2, 

 fungiform papillae. (After 

 Brubaker, from Kellogg, 

 Animals and Man. Cour- 



