PHARMACEUTICAL SOCIETY, EDINBURGH. 
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hibits where favoured by sunshine. The effect of light on the animal kingdom is not 
less decided. Tadpoles, when they are excluded from light, and whilst they may be 
supplied with abundance of proper food, and the water containing the air they require 
for respiration is a constant running stream, do not in the absence of light deve- 
lope themselves further into frogs, but remain tadpoles, increasing in size no doubt, 
but still only tadpoles,—in fact they become merely monster frog babies. During the 
hatching of the silkworms’ eggs, the influence of light is decided, as, in the dark, few 
of the eggs are hatched as compared with the number brought out in good light. Even 
human beings are influenced by light. The inhabitants of cellars and dark caves have 
a tendency to deformity, and the lighter our rooms are, and the more we are exposed to 
light, then there is the less liability to deformity. In the hospitals in London and St. 
Petersburg, it has been observed that in the wards which are best lighted, and es¬ 
pecially those which have a southern exposure, there are more recoveries of the sick, 
and these recoveries are more speedy than in the darker wards, including those having 
a northerly exposure. 
Electricity and magnetism likewise play an important relation in the animal king¬ 
dom. The electrical and magnetic changes in our atmosphere undoubtedly influence 
all organic structures, and much of the depression or elevation of animal spirits from 
day to day may be probably ascribed to such changes. The influence of electrical 
storms in souring milk, beer, soup, and other organic substances is well known, and it 
has been long observed that the passage of a lightning flash through the animal frame, 
not only causes death, but renders the body more liable to putrefaction, and probably 
also leads to the coagulation of the albumen of the blood and other juices and liquids. 
The relations which subsist between the physical forces and the vital activity of the 
animal, is only partly observable when we confine our attention to heat, light, and elec¬ 
tricity and other forces, as acting externally in the animal economy. It is only when 
these and similar forces are recognized to be present in the food or medicine which are 
partaken of internally, that a more full insight is gained into the dependence of vitality 
upon the physical forces. And even then comparatively little can be known or observed 
unless we carry along with us the important doctrines and conclusions derived from the 
study of the mode in which one force can pass into another. 
Modern scientific inquiry has done much to establish the two following points :— 
1st. That the food of the animal not only supplies material to build up the structure 
and to replenish waste, but that it also yields force which can be stored up in the animal 
economy and used, as necessity may require, in the display of vital energy. 
And 2nd. That all the physical forces—heat, light, electricity, motion, magnetism, 
and chemical affinity—are transmutable one into the other, and that they can directly 
and indirectly minister to the vital force of the animal. 
It will conduce to perspicuity in the study of this intricate and highly philosophical 
department of science if I refer first to the mutual convertibility of the physical forces, 
and thereafter observe the mode in which these can operate to sustain the vital activity 
of the animal. And I may state at once that the views held by scientific men on these 
points at the present day are mainly due to the labours of Mayer and Helmholtz on the 
Continent, and of Faraday, Grove, Jones, Thomson, and Tyndall in this country. 
The forces which have specially been experimented upon so as to exhibit the trans¬ 
mutation of one force into the other, are motion, heat, electricity, light, magnetism, and 
chemical affinity. Motion becomes heat when we rub or clap our hands; when two 
pieces of wood are rubbed against each other, as practised by uncivilized nations in order 
to procure fire ; when the blacksmith strikes rapidly the rod of iron till it becomes 
sensibly red-hot; when a nail is held to a grindstone in motion till the nail becomes 
unpleasantly warm, and when the badly greased axle of the railway carriage admits of 
sufficient friction being exerted between the axle and its bearings so as to raise these to a 
red-heat and set fire to the carriage. Motion becomes electricity when two pieces of white 
sugar, or two quartz pebbles, are struck together in a darkened room, and a luminous 
electrical glow is developed ; when two clouds rub against each other in the atmosphere, 
giving rise to one form of the lightning or electrical flash, and when a glass rod cr 
cylinder is subjected to the friction of silk, as in the ordinary frictional electrical ma.- 
chine. Motion can pass into light when the heat of friction is sufficiently high to 
appear as light. 
Heat becomes motion, as may be evidenced during the fusing of the metals when the 
