STREPTOTHRIX A CTINOMYCES. 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- 



