212 THE NERVOUS SYSTEM 



animal is in the scale of classification the smaller is the cerebrum. 

 The convolutions or creases in man's brain are more intricate 

 and deeper than those found in lower animals. These convolu- 

 tions give greater brain surface and contain more functioning 

 neurons. Scientists once thought that one man was more intel- 

 ligent than another because one had a heavier brain than the 

 other. But this does not seem to hold true. The brain of 

 Cuvier, a great scientist, weighed about four pounds, while that 

 of Gambetta, a French statesman, weighed only two and a half 

 pounds. Since mental defectives have been found with brains 

 weighing more than four pounds, weight alone does not mean 

 everything. The size and weight of a person must be taken into 

 account when considering weight of brains. 



Neurons never increase in number. The only growth possible 

 is the setting up of connections or synapses among the different 

 neurons. The more connections or synapses that are made, the 

 greater will be the number of mental processes, which is a factor 

 in determining the intelligence of animals. The ability to make 

 connections easily seems to be an inherited character. This may 

 account for the fact that some families have members more intel- 

 ligent than those of other families. 



One of the methods of studying the nervous system is through 

 experimentation with lower animals. Flourens and others have 

 observed that if the cerebrum of a pigeon is removed, the pigeon 

 loses all voluntarv or conscious action. It will not move toward 

 food nor away from danger. However, if food is put into its 

 mouth, it will swallow. When the cerebellum alone is removed, 

 balance and coordination become disturbed. The pigeon, if 

 placed on the edge of a table, will fall. It has difficulty flying be- 

 cause of a lack of balance and muscular coordination. Its volun- 

 tary activities, however, are intact. It experiences desire for food, 

 fear of danger, and other sensations. If the medulla is removed, 

 respiratory, circulatory, and heart actions cease and the bird dies. 



