348 PHYSIOLOGY CHAP. 



Gryus recorded the reaction time to auditory excitation in the 

 natives of Java and in Europeans resident in that island. He 

 found that this period was shorter in the case of natives and 

 became longer and longer in Europeans ; that is, the reaction time 

 increased in proportion to the length of their residence in the 

 tropics. Kohlbrugge regards this as a proof that a tropical climate 

 is injurious to the functions of the nervous system of Europeans. 

 This Dutch scientist, who bases his conclusions on empirical data 

 collected in his native country during three centuries of colonisa- 

 tion in tropical Asiatic islands, considers the climate of the tropics 

 to be ill-suited to Europeans, who after a prolonged residence in 

 such climates suffer from disturbances of the nervous system, such 

 as insomnia, irritability, inability to perform intellectual work, 

 debility, and neurasthenia. The data at our disposal relating to 

 the efficiency of the various organs of sense are relatively numerous ; 

 unfortunately, however, very little of this research work has been 

 done from the physiological point of view or with the accurate 

 instruments used by the physiologist. We will mention a few of 

 the more important conclusions. 



Owing to the glowing accounts given by various explorers of 

 the activity of the organs of sense, and more especially of sight 

 and hearing, possessed by certain primitive peoples, scientists came 

 to believe that these races were really endowed with organs of 

 sense of a higher order than those usually found in civilised nations. 

 Deniker states that the inhabitants of the Andaman Islands can 

 find certain kinds of fruit growing in forests at a considerable 

 distance solely with the help of the sense of smell. 



Kotelman (1884) says that the acuteness of normal sight, 

 measured by Snellen's method, increases in different races at the 

 rate shown in the following table : 



Germans 



Kussians 



Georgians . 



Ossetis and Calmucks 



Beggia-Nubians 



Andes Indians 



1-1 

 1-4 

 1-6 



2-7 



3 



5 



The sharpest sight was found in a Calmuck, 6-7. 



Recent and more accurate investigation tends, however, to 

 prove that there is no great difference in the acuteness of the 

 organs of sense in different races, a fact already noted by Fritsch 

 (1872) in the case of the natives of South Africa. 



Rivers (1905) made an accurate study of the organs of sense 

 of the Todas, determining in the case of the eye, sharpness of 

 sight, chromatic vision, and optical illusions; in taste, the 

 threshold of the four elementary tastes ; in the ear, sharpness 

 of hearing; in the nose, the acuteness of smell; in the cutaneous 

 senses the discriminative tactile threshold and the threshold of 



