1/6 The American Naturalist. [March, 
Micro-Organisms and Digestion.— The extensive re- 
searches which are now being carried on in regard to the rela- 
tions of bacteria to disease increase our interest in any addi- 
tion to our knowledge of their connection with the normal ac- 
tivities of the body. Drs. Harris andTooth, of St. Bartholemew's 
Hospital, have undertaken a series of experiments to investi- 
gate the relations of micro-organisms to digestion, and have 
published a preliminary communication on the subject.^ They 
find it easy to prove that proteids can be digested by pepsin 
independently of micro-organisms, but have not succeeded in 
establishing the converse proposition, namely, that micro-or- 
ganisms can of themselves convert proteids into peptone. In 
experimenting with trypsin it was found necessary to employ 
antiseptics in order to make sterile experiments. With mer- 
curic chloride, i to 2 per cent, neither peptone nor bacteria 
appeared, with carbolic acid, i to 2 per cent, peptone was abun- 
dant but bacteria absent; while iodine interfered neither with the 
digestion nor the development of bacteria. It was thus proved 
that the pancreatic ferment, like the gastric, can digest pro- 
teids without the aid of micro-organisms. 
It was found that the formation of leucin and tyrosin is 
probably due at least in part to the action of bacteria, and that 
the formation of indol seems to be entirely dependent upon it. 
The results of experiments indicate that there are special indol- 
forming organisms, in the absence of which this substance does 
not appear. 
These conclusions are in substantial accord with views which 
have been previously entertained, though hitherto they have 
been accepted without adequate experimental proof. — M. A. 
Johnson. 
PSYCHOLOGY. 
Observations on Putorius Vison.— On July 6, 1887, 
while engaged in geological work on the Cedar River, near 
Osage, Iowa, my attention was attracted by the peculiar act- 
ions of a Mink {Putorius vison.) By careful maneuvering, we 
were enabled to approach to within a short distance of where 
it was engaged, and there watch its behaviour unobserved. 
It was an old mother Mink engaged in fishing, for her young. 
^Journal of Physiology, vol. 9, No. 4. 
