438 ACTINOMYCETES. 



tion of temperature of 1. 5° to 2° or 2. 5° occurs after twelve 

 to fifteen hours. A French commission speaks especially 

 favorably of it (C. B. xix, 645). The reaction sometimes 

 is absent when the animal is extensively diseased, but for 

 these cases the reaction is not required. It scarcely ever 

 appears in healthy animals, and here it is to be remem- 

 bered that small areas are often to be found with diffi- 

 culty at the postmortem. The result is not influenced by 

 other diseases in cattle. Exceedingly rarely, latent tuber- 

 culosis is stimulated to new activity. It is of importance 

 that an animal often fails to give a positive reaction a sec- 

 ond time for a month after a typical reaction was first ob- 

 tained. 



The question does not appear to have been investigated 

 as to whether the tuberculin reaction occurs in animals in- 

 fected with Mycob. lacticola and Mycob. phlei. 



Naturally it is much more difficult to come to a con- 

 clusion regarding the reliability of the tuberculin reaction 

 in man, since it cannot be controlled subsequently by 

 thorough postmortem examinations; at any rate the injec- 

 tion of tuberculin in man for diagnostic purposes is not 

 employed to any great extent. 



3. Actinomyces. Harz, emend. Gasperini. 



Growths upon solid nutrient media are elevated, tough, 

 more or less wrinkled, often cartilaginous. Microscopi- 

 cally, they appear as long, thin, elongated mycelial threads, 

 the young ones with homogeneous contents without par- 

 tition walls, without a developed covering, and with abun- 

 dant, true branches. In older threads there can be dis- 

 tinctly recognized a delicate membrane, and within it the 

 colored contents, broken up into fragments. Positive cell 

 divisions are rarely observed in cultures of varieties of ac- 

 tinomyces. Some varieties, in the animal body, present 

 clubbed enlargements upon the ends of the radially ar- 

 ranged threads, which are to be explained as thickenings 

 of the sheath (see below). Man}' species form chains of 

 short colorless spores (conidia) upon thickened air hyphse 

 (two to ten times thicker than the threads) which rise 

 above the solid medium and compact culture film like a 



