$62 General Notes. (May, 7 
band. A smaller number collect under the yellow and orange 
rays and form there a pretty well-defined band. The few remain- 
ing forms are scattered in the more refrangible parts of the spec- 
trum and more especially in the green rays. For the violet rays 
the limits of sensitiveness of the Bacteria is not far from that of 
the human eye, but their appreciation of the ultra-red rays goes 
much beyond that of the eye. It is the ultra-red rays that are 
most abundantly absorbed by the Bacteria and which act most 
powerfully in exciting them to motion.—Pfliiger's Archiv., Bd. 30, 
a Os. 
Tue Diastatic ACTION oF SALIVA.—It has generally been be- 
lieved that the activity of the ferment fzya/in, which in normal 
human saliva rapidly turns starch into sugar, was arrested when 
the alkalinity of the saliva was neutralized or the fluid made 
slightly acid, and that therefore the conversion of starch of the 
food into sugar, which is begun in the mouth, was completely 
arrested when the food reached the acid juice of the stomach. 
The late work of Chittenden and Ely (Fourn. of Physiology, Vol. 
ii, p. 337), and of Langley and Eves (/éid, Vol. 1v, p. 18) has 
shown that the diastatic action of neutralized saliva is more rapid 
than that of the normal fluid, and that the addition of very 
minute quantities of sodium carbonate has a destructive effect 
upon the ferment, The former authors found that the addition of 
a small amount of acid, .025 p. c. HCl, destroyed toa great ir 
tent the starch converting power of saliva, but that when a sma 
quantity of peptone was also added, the diastatic action of the 
ferment was increased above the normal, Langley and Eves 
point out that the peptones probably exert their favorable influ- 
ence through combining with the free acid added to the saliva, — 
thus preventing its destructive influence upon the iptyai 
they find that the slightest amount of free acid in the mi 
arrests the ferment action. cee 
There is good reason to suppose that the gastric juice $ 
during the first three-fourths of an hour after the beginn l 
“ digestion contains little if any free acid; so it is highly. prove 
that the diastatic action of saliva continues for some timer is 
the entrance of food into the stomach, though it seems tained . 
that the salivary ferment is finally destroyed by the acid, COn 
in the gastric juice. je 
xture 
ing of 7 
—The background of conscious perception, physiologically © y um 
ing, is defined by W. T. Sedgwick as “that standard a which 
consciously held) with which we compare any suo ii 
awakens consciousness,” We perceive difference of restri 
d. The latter 
tensity between a specific stimulus and its background. *"" aous- 
may vary so that a stimulus which will to-day rome ying 
ness or motion will not do so to-morrow. Instea ze 
