219 
nessee, Kentucky, Ohio, Indiana, and Illinois have suffered the most 
severely. At the present time cases occasionally occur in Tennessee 
and North Carolina. Cases have been reported in Illinois as late as 
1904. The recent discovery of the disease in New Mexico is the first 
indication we have of its occurrence west of the Mississippi Valley. 
In the endemic foci, the disease in the lower animals is limited to 
I jj rather well-defined areas. Many of these areas are fenced to prevent 
the access and consequent contamination of stock. I have seen a 
■ number of such inclosures varying in size from an acre to several 
i| thousand acres. “ Milksick Mountain,” in Mdiite County, Tenn., is 
J entirely inclosed by a fence 7 or 8 miles in length, built about fifty 
years ago; since Avhich time the disease has been very rare in that 
j locality. 
! The infected areas are alwaj^s wooded land, but otherwise vary 
I markedly, from dark damp ravines to high dry ridges or ordinary 
level forest tracts. Seaton (1841), who wrote extensively on the sub- 
ject, claimed that the disease was found only where sandstone entered 
largely into the composition of the soil. Other writers do not agree 
with this view. 
There appears to be a very general agreement in the opinion that 
wooded land is essential for the existence of the disease and the clear- 
. ing of the land suffices to remove all danger of animals acquiring 
trembles. It is said that if land be rendered harmless by clearing, 
then be permitted to produce a new growth of timber, the tract may 
again become the seat of the disease. So sharply are some milk-sick 
areas defined that farmers point out places where on one side of a 
! fence animals may be pastured in perfect safety, whereas if pastured 
on the other side of the fence they are almost sure to contract trembles. 
j I have been told of more than one outbreak of trembles due to chang- 
1 ing the fence of a pasture by a few yards so as to include some wild 
; (uncleared) land. 
It has been claimed that springs and water courses have conveyed 
, the cause of trembles, but it seems clear that in such cases the animals 
contract the disease in the surrounding wooded areas. 
I Etiology and pathology . — Children appear to be less liable to the 
disease than adults. Nursing women are said to enjoy a relative im- 
munit}’’ (Johnson, 1866). One attack confers no immunity; in fact, 
it appears to predispose to subsequent attacks (Philips, 1877). 
I The disease occurs most frequentl}^ in the spring and the fall, but 
records of cases in summer are not rare and a few are said to have oc- 
curred in winter. Drake (1841), who investigated the subject in 
Ohio, states that the disease occurred in May and June, but was more 
frequently met with in August, September, October, and November. 
I The majoritv of writers agree with this, stating that cases are most 
