376 BACTERIOLOGY. 



first accorded to it. Its field of usefulness is now 

 almost limited to the diagnosis of obscure cases, and 

 even for this purpose it is less frequently employed 

 than formerly. 



In veterinary medicine it has proved much more 

 trustworthy as a diagnostic aid, and is practically 

 everywhere in use for the detection of incipient tuber- 

 culosis, especially in cattle. 



VACCINATION AGAINST TUBERCULOSIS. Recent 

 experiments by v. Behring, Pearson and Gilliland, and 

 others have shown that it is possible to immunize ani- 

 mals with lowly virulent tubercle bacteria of human 

 origin, and after one or two injections with such organ- 

 isms the animals show a marked degree of tolerance to 

 the more highly virulent bovine organisms. The 

 results of experiments in this direction have been so 

 encouraging that it is probable this method may be 

 utilized for the active immunization of cattle against 

 tuberculosis. 



ACTINOMYCETES. 



The term actinomycetes is restricted to a group of 

 organisms having morphological affinities with the bac- 

 teria on the one hand and the hyphomycetes on the 

 other. They resemble the bacteria in that they occur 

 as homogeneous threads which under artificial cultiva- 

 tion may become segmented into short bacillus- or 

 coccus-like fragments. Furthermore, they are unlike 

 the moulds in that they have not a double wall ; are not 

 filled with fluid containing granules, and the segments 

 are not separated from one another by a distinct parti- 

 tion. They simulate the moulds in that they develop 

 from spores into dichotomously branching threads, 



