1885.] Fhysiology. 907 
y 
vitellus, lead, in certain cases, to very remarkable modifications 
of embryonic development. 
The foregoing scheme deals more especially with the evolution 
of the various higher types of development, and if the way in 
which these have grown out of the lower ones has been made a 
little less obscure than hitherto, my object in writing this will have 
been attained. The manner in which placentation has been modi- 
fied is also a fruitful subject for farther investigation, not less so, in 
fact, than the question as to how the amnion arose. The facts of 
embryology tend to show that the amnion is the result, as stated 
above, of the gradual invagination of the embryo into the blasto- 
dermic vesicle. The invagination begins at the head end of the 
embryo ; the amnion, as is well known, always developing its 
first traces at ‘the cephalic end of the embryonic disk. It is also 
probable that the cavity of the false amnion is the homologue of 
the cleavage cavity of certain of the lower forms — ¥ohn A. 
Ryder. 
PHYSIOLOGY. 
A CONTRIBUTION TO THE KNOWLEDGE OF PeEpstn?.—Sundberg 
has hit upon a method for preparing pepsin, which gives results 
better than those obtained by Briicke’s method. . 
Calves’ stomachs are taken, the pyloric portion removedand the 
remainder of the mucous membrane carefully washed with water. 
The superficial portion of the membrane is then scraped off with 
a watch glass, and the substance thus obtained is ground up with 
a weighed quantity of salt. Enough water is added to this to 
make a saturated solution of salt. After standing 24-72 hours 
this was filtered and the Na Cl removed by dialysis. The dialysed 
liquid contained very little albumin and had a very powerful 
peptic action. It was further purified by being kept at 40°C. 
for some time to destroy the rennet ferment, and was then 
allowed to digest itself for one or two weeks, until all the albumin 
was converted into peptone. To this liquid chloride of calcium 
and acid sodium phosphate were added, and the liquid made 
' This department is edited by Professor HENRY SEWALL, of Ann Arbor, Mich. 
*Zeitsch. f. physiol, Chemis. 9, 319. Sundberg. 
