STREPTOTHRIX ACTINOMYCES. 617 
keeping the cultures for a week or more the colonies 
run together and form a thick, wrinkled mass which 
sinks into the media. The individual colonies are 
yellowish .to red in color, and are covered by a whit- 
ish, fluffy down, consisting of cobweb-like threads. 
On touching the colonies they will be found to cling 
close to the medium, and on forcible removal they go 
to pieces. On making a smear preparation the thread- 
like structure will be seen. In stick cultures the growth 
usually presents a tree-like appearance, but it varies 
very considerably; there may be no reddish pigmenta- 
tion, and the cobweb-like threads are not always devel- 
oped on the surface. Occasionally the culture on agar 
is colored brown. 
The Growth in Bouillon. When the medium is allowed 
to stand perfectly still a distinct granular growth occurs, 
but on agitation these grains are broken up, though the 
liquid is never clouded. At times large flakes or a mem- 
branous film form on the surface of the medium, upon 
which develops the fluffy down previously described. 
The Growth on Potato, On this medium the growth 
is somewhat slower, resulting in a thick, viscid, mem- 
branous deposit on the surface of the potato on which 
the same cobweb-like threads are developed. The color 
is yellowish-red. . 
The cultures are quite resistant to outside influences; 
dried they may be kept for a year or more; they are 
killed by a temperature of 75° C., the time of exposure 
being five minutes. 
Occurrence in Animals. Actinomycosis is quite prev- 
alent among cattle, in which it occurs endemically; 
it is more rare among swine and horses, and is some- 
times found in man. The disease is probably not con- 
