Pathogenesis 381 



pearance from the formation of short aerial hyphae. The 

 best growth occurs when free access of oxygen is permitted. 



Blood-serum. Upon blood-serum the nodular growths 

 present a yellowish or rust-red color, and are surrounded 

 with a whitish down of fine threads. The colonies adhere 

 closely to the culture media and are so firm that they crush 

 with difficulty. If the surface be scraped, spores and fine 

 threads may be secured. If the mass be crushed, branched 

 filaments may be secured. The colonies become confluent 

 in the course of time, and a thick wrinkled membrane is 

 produced. The growth liquefies blood-serum. 



Gelatin. In gelatin puncture cultures an arborescent 

 growth occurs and the gelatin is liquefied. 



Agar-agar. Upon agar-agar and glycerin agar-agar the 

 growth is similar to that upon blood-serum. The agar-agar 

 turns brown as the culture ages. 



Bouillon. In bouillon the growth occurs in the form 

 of large granules if allowed to stand quietly; of numerous 

 small granules if frequently shaken up. The granules are 

 similar in structure to those formed upon the dense media. 

 The bouillon does not become clouded. 



Potato. Upon potato the growth resembles that upon 

 blood-serum, but is slower in developing. The color is red- 

 dish-yellow and the white down early makes its appearance. 



Eggs. The organism can also be grown in raw eggs, into 

 which it is carefully introduced through a small opening 

 made under aseptic precautions. In the eggs long, 

 branched mycelial threads quite unlike the bacillary forms 

 that grow upon agar-agar are formed. 



The characteristic rosettes so constantly found in the tis- 

 sues are never seen in artificial cultures. 



Virulence. When the actinomyces is grown upon artifi- 

 cial media the virulence is retained for a considerable time. 



Pathogenesis. Actinomycosis is almost peculiar to bo- 

 vine animals, but sometimes occurs in hogs, horses, and 

 other animals, and rarely in human beings. The disease 

 can with difficulty be inoculated into experiment animals, 

 the introduced fungi either becoming absorbed or encap- 

 sulated by connective tissue and not growing. In the 

 abdominal cavities of rabbits the peritoneum, mesentery, and 

 omentum show typical nodules containing the actinomyces 

 rays in cases of successful inoculation. 



Mode of Infection. The manner by which the organ- 

 ism enters the body is not positively known. In some cases 



