98 
POPULAR SCIENCE REYIEW. 
The eminent Greek physician considered digestion as a cooking process. 
Galen maintained the existence of three kinds of digestion, the first 
performed in the stomach, the second in the duodenum, and the third in 
the liver ; a view taken in later times by Servetus and Drake. Plistonicus, 
a disciple of Protagoras, identified digestion with putrefaction. Hilmon 
regarded digestion as fermentation, and divided it into six kinds, a view 
in which he was followed by Sylvius, Willis, Boyle, and others. The 
mechanical theory of Borelli, Bcerhaave, and Pitcairn considered digestion 
to be mere trituration, a view which, as far as animal food was concerned, 
was experimentally refuted by Reaumur. This naturalist introduced into 
the gizzards of birds portions of meat enclosed in perforated metal tubes. 
On killing the bird after some time the meat was found to have been 
dissolved. Seeds, however, enclosed in a similar manner, resisted the 
digestive process. Spallanzani succeeded in withdrawing gastric juice 
from animals, and by its means performed artificial digestion outside the 
living body. The author concludes with a notice of the observations made 
upon the celebrated Alexis St. -Martin, who, as is well known, had a per- 
manent hole leading from without inward to his stomach, so that 
substances could be readily introduced into his stomach, and withdrawn 
from it. 
Detection of Blood by finding its Crystals. — This is a much easier process 
than has been thought, and is also much more generally applicable. In 
blood decomposed, or that has been treated by acids or caustic alkalies, 
haemoglobin is changed into a new substance ; hsematin is formed, which, 
combined with hydrochloric acid, gives characteristic crystals. In order to 
obtain them we must proceed thus : A small fragment of dried blood is 
placed on a glass slide ; it is dissolved in a drop of water, and a minute 
portion of sea-salt is added. It is covered with a thin slide, and pure 
acetic acid made to pass between the two slides, and it is heated over a 
spirit-lamp to boiling-point. Acetic acid is again added, and it is heated 
afresh, and this is repeated till the crystals are obtained. They are 
rhomboidal, of a dirty brown colour, quite characteristic, and require to be 
seen with a magnifying power of three hundred or four hundred diameters. 
With the smallest quantity of blood this reaction can always be produced. 
Effect of the Injection of Acid into the Brain. — A valuable paper on this 
question has been contributed to a late number of 16 Virchow’s Archiv,” 
from which the u Academy ” makes a long extract, which we shall take in a 
shorter form. Nothnagel injected acid in the first place into the hemispheres 
of the brain of a rabbit. He found the animal remained quiet during the 
operation, and was subsequently lively and ate well. Its motility was 
apparently undisturbed, and no sensory disturbance could be detected. If 
the injection were made into the left hemisphere the right forefoot could be 
placed in any position, provided this were done slowly, without its being 
retracted, though similar attempts with the left forefoot were promptly 
resisted. The animal will sometimes remain in an abnormal position for 
several minutes. If the skin be slightly pinched the leg is, however, 
immediately retracted. When the animal lived over a week or so this 
peculiar condition became less and less marked. There was no correspond- 
ing condition in the hind limbs. A similar experiment on a dog gave the 
