826 General Notes. [September, 
PHYSIOLOGY.’ 
Tue DELICACY OF THE SENSE OF SMELL.—The sense of smell is 
probably the leading sensorial endowment in most insects, and it 
oes for them what sight and hearing do for man. Its potency in 
helping along intelligence is very great, since we know that men- 
tally insects stand at the head of the invertebrate, as man stands 
at the head of the vertebrate world. The sense of smell is prob- 
some twelve square feet. The sense falls in value in the Amphi- 
bia, reptiles and birds, but rises again in the Mammalia, though 
not in proportion to intelligence. Its extreme acuteness In the 
og, the most intelligent of animals short of Quadrumana, !s well 
known. In man, the sense of smell is subordinate, and even rudi- 
mentary. Olfaction adds to man’s enjoyment, preserves him from 
some dangers, but does not very much extend his knowledge of 
his environment. : 
Yet despite the comparative insignificance of this sense in man, 
its delicacy is most marvelous, and by it we can appreciate more 
minute subdivisions of matter or the impact of more infinitesimal 
molecular vibrations than by any other of the avenues to the 
rain. 
Professor Valentine has made some interesting and striking €x- 
periments in proof of this. He found that a current of air con 
taining 1-30,000 milligramme of bromine, or 1-500,000 ome! 
gramme of sulphureted hydrogen, or 1-2,000,000 milligramme ` 
oil of roses could be perceived by the sense of smell. He also 
determined that the amount of odoriferous air which must pasi 
over the olfactory membrane in order to excite the sense of s 
was from fifty to one hundred cubic centimeters (one-tenth to pee 
fifth of a pint). He calculated, therefore, that the actual panto 
of bromine necessary to excite a sense of smell was 1-6000 a A 
gramme, of sulphureted hydrogen 1-5000 milligramme of o 
roses 1-20,000 milligramme (about 1-120,000 of a grain). 
Two recent experimenters, E. Fisher and F. Pentzoldt, 
the cubic centimeter of chlorphenol, and 1-23,000,000,000 ae 
gr e of mercaptan, these substances could be appreciated, si 
it was estimated that only 1-4,600,000 milligramme of chlorp n 
nol, and 1-460,000,0co milligramme of mercaptan, 1S necessary pe 
excite a sensation of smell. There exists, therefore, a substan 
_ which in so small a subdivision as 1-2,760,000,000 grain, 
‘This department is edited by Professor Henny SEWALL, of Ann Arbor, 
or not 
Michig2™ 
A TEN EELA 
