MENTAL DIFFERENCE AND DISORDER. 193 



Quantity, 

 Quality, and 

 Distribution. 



The brain and its membranes. 

 Other parts of the nervous system. 

 Various other bodily organs or functions, in- 

 cluding especially 

 The reproductive. 

 The stomach and bowels. 

 The skin and its accessories. 

 The heart and blood-vessels. 



3. The results of the action of poisons and drugs, 



especially on the brain and nervous system 

 including the bites and stings of snakes, in- 

 sects, or other animals. 



4. The effects of mechanical injury or irritation, 



including the presence of foreign bodies, 

 castration, oviposition. 



5. The results of consanguinity in alliances. 



III. Exposure to atmospheric or climatic influences, in- 

 cluding 



Temperature especially its changes, and the ex- 

 tremes of heat and cold. 

 Light especially its absence or deficiency. 

 Electrical conditions. 



IV. All sensorial impressions especially certain 



Colours, Smells, and 



Sounds, Sights. 



Examining in detail the extent and mode of operation of 

 some of the leading causes above tabulated, it has in the 

 outset to be noted that, as a general rule, they play very 

 much the same parts in the production of mental difference, 

 disorder, or decay in other animals that they do in man. 



Thus old age has the same mental and physical accompa- 

 niments in other animals as in man. There is the same 

 gradual decadence of mental and bodily vigour ; the same 

 loss of memory and confusion of ideas ; the same loss of 

 mental aptitudes or accomplishments ; the same tendency to 

 childishness and fatuity ; the same degeneration of the 



VOL. II. O 



