SCIENTIFIC SUMMARY. 
329 
The Hairs of the Lower Mammals. — Dr. Hoffmann, in an essay on this 
subject, says that in the hair of the lower mammals we find generally the 
same three layers as in human hair, but differing to such a degree that, as a 
rule, a hair can be easily recognized as belonging to an animal. The cuticula 
in most animals has absolutely and relatively larger cells, which give the 
hair a characteristic appearance, as is seen especially well in the wool from 
sheep. A toothed or saw-like appearance of the contour of certain animal 
hairs depends upon the larger development and peculiar relations of the 
cuticular cells, whose points stand out so far from the hair that the latter 
has a feathered appearance, as in a field-mouse. Among animals the greater 
bulk of the hair is formed by the medullary substance, the cortical substance 
being only a thin layer ; often, indeed, is reduced to a hem-like streak. 
This predominance of the medullary substance is seen best in the shaft of 
the hair ; towards the end the cortical substance predominates, the me- 
dullary becoming thinner. Generally the cortical substance has the same 
structure as in human hair, and the same variety of pigmentation ; in some 
animals, as the cat, rat, and mouse, the cortical substance is more translucent 
and of finer structure, resembling, under the microscope, a hyaline envelope 
of the medullary substance. The medullary substance in animals is an 
interesting study, differing greatly from the same layer in human hair. The 
cellular structure is generally very evident, without the employment of any 
reagent. The cells vary greatly in size and form. 
PHYSICS. 
Frost Striations in Mud . — The Rev. F. R. Goulding, in a communication to 
i( Silliman’s American Journal” for March 1874, asks the privilege of call- 
ing attention to a natural phenomenon which has long enlisted his interest 
and that of a few others, but which remains, so far as known, without ex- 
planation. It is that of slight but plainly marked striations of the soil after 
a freezing, looking as if a very light harrow had been drawn over it from 
north-west to south-east, leaving irregular furrows, varying from half an 
inch to an inch and a half in depth, and from centre to centre. His atten- 
tion was first drawn to it in 1854, in Upper Georgia, during and after the 
thawing of an extensive and severe 11 black frost.” After residing for ten 
years in a region where there were no black frosts, and of course no striations, 
he returned to the mountains of Georgia, and was soon reminded of former 
observations by seeing the soil of his garden very deeply marked the same 
way as before, during, or rather toward the close of a hard freezing. This 
place is about forty miles distant from the other, and the soil wholly 
different, that being limestone and this granite. These striae invariably 
run from north-west to south-east, and this is so in shaded as in sunny 
places, and whether the wind at the time blew, or whether the air was still. 
They begin to appear before the frozen surface has thawed. Further, the 
direction is at right angles to the stratification of the country, the out-crop- 
pings of the rocks being here in a line from north-east to south-west. If 
this coincidence be connected with the cause of the striations, it is in some 
