42 OF VITAL MOTION. 



appears also when we attend miDutely to the history 

 of the latter function. If we are to estimate the 

 vigour of the respiratory changes by the amount of 

 the gaseous products which are given off, it is found 

 that this vigour is directly proportionate to the feeble- 

 ness of the vitality of the organism, becoming more 

 and more marked as the vitality flags, and by insen- 

 sible degrees blending at death into the signs of com- 

 mon decay. The plant, also, lives less intensely at 

 night than during the day, and at this time the greater 

 amount of carbonic acid exhaled is the evidence of 

 increased freedom in the respiratory changes; and in 

 autumn, when the powers of vegetation are sickening, 

 the quantity of the same gas is greater than during 

 the summer. In animal bodies, also, the products of 

 expiration are greater in winter than in summer ; and 

 in tropical regions, where the powers of the system 

 are fortified by a free exposure to the sun, the deepened 

 colour of the skin may be an argument in favour of a 

 certain decomposition of carbonic acid, under the influ- 

 ence of light, and of a deposition of carbonaceous matter 

 in some degree analogous to that which takes place 

 in the chlorophyllous cells of plants. Again, in the 

 depression of putrid and eruptive fevers, the exhala- 

 tion of gases from the pulmonary organs is much 

 greater than in health. 



The conclusion from these facts is that the process 

 of respiration is resisted by the vitality of the organism, 



