ON THE PHYSICAL CONSTITUTION OF THE SUNBEAM. 41 



one been experimentally determined by direct experiment by Dr. REID (Carpenters 

 Human Phys., p. 417). 



134. We might now proceed to inquire what, on these chemical principles, ought to 

 take place when a reverse action ensues, as when between the arterial blood and the 

 tissues through which it flows those conditions are set up which lead to its more rapid 

 deoxvdation, and the concomitant evolution of heat ; conditions which are found in 

 the various local inflammations. In these, by reason of an increased affinity between 

 the soft tissues and the arterial blood, deoxydation and corresponding combustion more 

 rapidly take place, with an abnormal elevation of temperature, and the flow of blood 

 to the point of disturbance is increased. The old medical aphorism, u ubi irritatio ibi 

 ajfluxus.'' translated into the precise language of modern chemistry, simply means, to 

 the point where its deoxydation u taking place, the arterial blood trill jloir. 



135. By the aid of the principles here laid down, all the various physiological or 

 pathological conditions which are met with in inflammation, rsphyxia, gangrene, &c., 

 are presented as so many interesting chemical problems for solution. Such cases, also, 

 as the non-asphyxiation of reptiles, the variable respiration and heat of insects, accord- 

 ing as they are in motion or at rest, the results of death from lightning, afford abundant 

 opportunity for the full verification of these doctrines. That the time has now ar- 

 rived when the exact sciences are to come to the aid of physiology, no one can doubt. 

 For many centuries past, a profitless system has been followed, the same system that 

 formerly obtained in natural philosophy, and the uncertainties and doubts of medical 

 science are the best proofs of its value. It is the ruling principle of this system to sat- 

 ibfv the inquirer for facts by the use of empty words, words which mean nothing and 

 prove nothing. Life and vitality, with other sonorous epithets, figure away in these 

 visionary speculations as though they were realities, and change their forms without 

 reason or rule, as do the images that we see in dreams. 



CHAPTER IV. 



ON THE PHYSICAL CONSTITUTION OF THE SUNBEAMS AND ON THE PRISMATIC SPECTRUM. 



CONTENTS: Modes of isolating the Coloured Rays. Newton's Prismatic Spectrum. 

 Theory of the Co/ours of Light. Illuminating Calorific and Chemical Pmctrs of the 

 Spectrum. Newton's Processes for purifying the Spectrum. Fixed Lines. Mellon? s 

 Experiments on the Distribution of Heat. Physical Independence of Heat. HerscheFs 

 Experiments on the Thermic Spectrum. Chemical Action of the different Regions 

 of the Spectrum on a Daguerreotype Plate. Chemical Action on other Bodies. 



136. FROM the foregoing observations (Ch. I.); we see that the primary formation 

 of organized from inorganic matter is brought about by the agency of the sunbeam, 

 eiiher directly falling on the point of change, or received in an indirect way, as the 

 diffused light of the sky or cloud's (56). 



F 



