November 2,1872.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
315 
summing up the general results of his laborious re¬ 
searches on vegetable physiology, says, “ Si l’on envi¬ 
sage la vie vegetale dans son ensemble, on est convaincu 
que la feuille est la premiere etape des glucoses que, 
plus ou moins modifies, on trouve repartis dans les 
di verses parties do Torganisme; que c’est la feuille qui 
les elabore aux depens de l’acide carbonique et de 
l’eau.— Ann. de Chimie , tom. xiii. p. 415. The funda¬ 
mental chemical reaction taking place in the leaf may 
therefore be represented as follows : — 
(1) CO, 0 + H.,0 = CO, H, + 0,0 
(2) 6(CO.H 2 ) ' = C 6 H 12 0 6 . 
In the first equation carbonic acid and water are simul¬ 
taneously attacked, with the liberation of a volume of 
oxygen equal to that of the original carbonic acid, to¬ 
gether with the formation of a substance having the 
composition of methylie aldehyde. The second equation 
represents the condensation of this aldehyde into grape- 
sugar. The transformation induced in (1) necessitates 
the absorption of a large amount of energy; and if we 
neglect the heat evolved in the combination of nascent 
CO and H^, which can be shown to be very little, the 
calculated result is made a maximum ; whereas the con¬ 
densation of (2), being attended with an evolution of 
heat, diminishes considerably the amount of power re¬ 
quired. Happily, Franklin’s direct determination of the 
thermal value of grape-sugar leaves no doubt as to the 
true equivalent of work done in its formation. Taking 
the following thermal values, C0,0 = 68,000, H 2 ,0 = 
68,000, C 3 H J2 0 6 = 642,000, 1 cub. bentim. of C0 2 de¬ 
composed as in (1) would require 6-06 gramme-units of 
heat, or its light-equivalent, whereas the complete change 
into grape sugar of the same amount of carbonic acid re¬ 
quires only 4*78 gramme-units. But, we have seen before, 
1 square decimetre of green leaf functions at the rate of 
5'28 cub. centims. of carbonic acid assimilated per hour; 
therefore, 5*28 X 4*78 = 25*23 represents the number 
of gramme-heat units conserved through the absorption 
of light in the above period of time. Pouillet estimates 
the mean total solar radiation per square decimetre ex¬ 
posed normally to the sun’s rays in or near Paris per 
hour as 6000 gramme-units, so that 6000 -h 25*23 =* 
UFa represents the fraction of the entire energy con¬ 
served. The estimate is by no means too great, as 
Boussingault has shown the leaf may function at twice 
the|above rate for a limited time; and as both sides of 
the leaf are included in the measurement of the green 
surface in his memoir, we ought to double the fraction 
for a leaf exposed perpendicularly to the sun’s rays, in¬ 
creasing the above number to the 120th part. 
In connection with equation (1), above given, as repre¬ 
senting the action of sunlight on the leaf, it is worthy of 
remark that, supposing the carbonic acid and water 
equally efficient as absorbing agents of the vibratory 
energy (although each has a specific absorption for cer¬ 
tain qualities of rays), the decomposition of the two com¬ 
pound molecules may take place continuously side by 
side, owing to the equality of the thermal equivalents 
of carbonic oxide and hydrogen. We already know, 
from the laborious researches of Tyndall, how thoroughly 
aqueous vapour retains thermal radiations; and Janssen 
has further shown the same substance has a strong 
absorptive action on the rays of light of low refrangibility 
(just those rays that are in part selected by chlorophyl), 
producing the well-known atmospheric lines of the solar 
spectrum. The presence, therefore, of varying quan¬ 
tities of aqueous vapour in the atmosphere in all proba¬ 
bility produces a considerable difference of rate in the 
decomposition effected by the leaf, and may in fact end 
in carbonic acid and water being attacked in another 
ratio than that given as the fundamental equation of 
decomposition. Thus the same plant in different atmo¬ 
spheric conditions may elaborate different substances. 
ODOURS.* 
BY M. FEBNAXD PAriLLON'. 
The subject of odours, considered in the light of recent 
discoveries in chemistry and physiology, has been re¬ 
cently discussed in an interesting memoir by M. Fernand 
Papillon. The paper is too long to be reproduced entire 
in these pages; we must, therefore, be content with 
extracting some of its more salient points. In doing so, 
we shall merely indicate the arguments in the physiologi¬ 
cal portion, giving to the physical and chemical portion 
the greater prominence that is in keeping with the 
object of this Journal. 
The seat of the sense of smell is the pituitary mem¬ 
brane which covers the inside of the nostrils. It is a 
mucous surface in which a certain number of nerves 
terminate in delicate ramifications, and is kept constantly 
moist by a liquid which it secretes. The mechanism of 
smelling appears to consist in the contact of air-borne 
odoriferous particles with the olfactory nerve; if the 
passage of air be interrupted, the sensation is not ex¬ 
perienced. The sense of smell varies very much in 
different individuals, being sometimes without any ap¬ 
parent cause absent altogether ; in other cases there is 
insensibility to certain odours, analagous to Daltonism 
in the sense of sight. A close connection exists between 
smelling and tasting, and it has been shown that many 
tastes are the result of a combination of olfactory and 
gustatory sensations. In reality there are but four 
primary and radical savours, viz. sour, sweet, salt and 
bitter; and if a variety of sapid substances be tasted 
while the nostrils are closed, or while the pituitary 
membrane is out of order, it will be found that the 
tongue only perceives these four sensations. 
In 1799 Prevost first pointed out that certain odorous 
substances, both solid and fluid, when placed upon a piece 
of wet glass or in a saucerful of water, act immediately 
upon the molecules of the liquid with which they come 
in contact, and in dispersing them give rise to more or 
less of a vacuum. In later years, these movements of 
odorous substances on the surface of liquids, have been 
studied by M. Liegeois. He found that the majority of 
these bodies execute various gyratory and other move¬ 
ments analogous to those of camphor upon the surface of 
water; but that while some, such as benzoic acid, 
succinic acid, and bitter orange peel comport themselves 
in an exactly similar manner, the movements of others 
cease more quickly, since they rapidly become surrounded 
by T an oily medium in which they are imprisoned. It 
was found necessary to reduce them to powder to produce 
the same phenomenon. When experimenting upon 
liquid substances, M. Liegeois saturated very light, 
spongy and odourless seeds with them, and these when 
thrown upon water underwent the same movements. 
From a series of observations, methodically conducted, 
he came to the conclusion that these movements are not 
due to a disengagement of gas causing a recoil, but to 
the separation and rapid diffusion of odorous particles 
into the body of the water. The phenomenon depends 
exclusively upon the affinity of fluids for these particles, 
and also for those of fatty matter. For instance, M. 
Liegeois found that a drop of oil placed on the surface 
of water parts with an enormous number of microscopic 
particles without sensibly diminishing in volume, and 
that aromatic essences give the same result. However 
insoluble in water they have an energetic tendency to 
become diffused through it, and it suffices for water to 
receive the odorous principle in an extremely delicate pro¬ 
portion to acquire all its perfume. Thus it is that while 
the flowers are covered with the glistening drops of dew, 
or after a slight shower, they* exhale the sweetest and 
freshest perfumes. So also in the phenomenon of smell¬ 
ing j the air carries the odorous particles into contact 
* Abstracted from a memoir, entitled‘Les OdeursyTapres 
lea Decouvertes Recentes de la Chimie et de la Physiologic 
(Moniteur Scientifique-Quesncville, xiv. 298 et seq.). 
