124 TRINIDAD. 



Average quantity of rainfall in Demerara (5 years), 75*62 ; 

 Berbice, 70-53; St. Vincent (8 years), 99*36 ; St. Christopher 

 (13 years), 5223; Barbadoes (26 years), 57*74. 



I have already stated that the aforesaid physical agencies- 

 but particularly light, heat, and humidity — exercised the greater 

 influence on animal as well as vegetable life ; I will now briefb 

 examine their influences on our own organs. 



Heat. — Besides its well-known debilitating effect on th( 

 human body, a high temperature seems to have a powerfi 

 action in modifying certain functions. Under such temperature, 

 the cerebral activity is diminished, as well as the muscuh 

 power, and the digestive organs are greatly enfeebled. Cutaneoi 

 exhalation is much increased, and becomes apparent under the 

 form of perspiration; in fact, it is brought to its summum in 

 a warm and damp atmosphere. Perspiration has, for effect, a 

 diminution of the quantity of heat produced in the human body 

 by natural processes — nor does it act as a debilitating cause, to 

 the extent that is generally supposed ; for prostration of strength 

 is relieved by an abundant natural perspiration, and its increase, 

 when the air is not too damp, results in a counteraction of the 

 effects of a high temperature. I may adduce, as a proof of 

 what I advance, that individuals in robust health are generally 

 those who perspire the most. It is a principle in physiology, 

 that the greater the activity of an organ the more liable it 

 becomes to disease ; and, as a consequence, cutaneous affec- 

 tions must be more frequent and serious in a warm than in a 

 temperate climate. 



Humidity. — Warm air contains, even when comparatively 

 dry, a larger contingent of water than cold damp air. This 

 aqueous admixture increases the volume of air, and diminishes 

 its specific gravity ; as an inference, warm damp air contains 

 less of the respirable element than any other. The warmer the 

 atmosphere the larger the quantity of water which it can hold 

 in suspension. A damp atmosphere — the temperature being 

 equal, or even greater — produces a peculiar feeling of chill, 

 widely differing from the bracing effect caused by a cold, dry 

 air. The sensation produced by the former is keener, and seems 

 to penetrate the whole system, thereby producing chilliness and 

 involuntary shivering from within, with a bluish paleness 

 externally ; in fact, a damp atmosphere acts by diminishing the 



