THE 



GARDENER'S MAGAZINE, 



JULY, 1843. 



ORIGINAL COMMUNICATIONS. 



Art. I. Comparative Physiology. By R. Lymburn. 



{Continued from p. 215.) 



In Chap. II. On Vital Stimuli, Dr. Carpenter says : — "It has 

 been shown in the last chapter, that the actions of living beings 

 dej)end on an organised structure possessing vital properties, and 

 certain agents necessary to call the operation of these properties 

 into existence. In the higher classes especially, of living beings, 

 the influence of the stimuli supplied by alimentary materials, heat, 

 light, electricity, &c., is directed towards the preparation of a 

 nutrient fluid, which contains the elements of all the solid 

 tissues of the body, and which not only supplies the materials 

 of growth, but stimulates the organs to the performance of their 

 actions. Light, heat, &c., serve as external stimuli, and their 

 immediate action is upon the simplest of the organic processes. 

 The nutrient fluid is the chief internal stimulus to the nu- 

 tritive actions of the system, assisted by the continued influence 

 of external agents. The motion of the blood through the lungs 

 is as dependent upon the influence of the air in the cells, as 

 sneezing is uj)on a stimulant applied to the nostrils ; and, if the 

 circulation be suspended, the nerves and muscles lose their 

 power, from the want of the stimulant action of the blood. 

 Both the external and internal stimuli must thus be regarded 

 as vital, as they not only give rise to vital actions, but these 

 actions conduce to the maintenance of life. The action of the 

 internal stimuli will be best considered under the functions of 

 absorption, nutrition, respiration, &c. The dejjendence of life 

 on the external stimuli, heat, light, electricity, &c., is greater in 

 proportion to the perfection of the structure, and the variety of 

 its organs, and vice versa. Beings of a simple organisation 

 are capable of enduring a deprivation of these stimuli, which 

 would be fatal to those higher in the scale ; as the more de- 

 veloped the parts of the system are, the more closely are the 

 parts connected with one another. 

 3d Ser. — 1843. VI I. z 



