HISTOIUCAI, KACKCKorXI) 



Tahi.k 1 

 Species of aclinomyceles recuynized in 1893 (u 1894 ^U Gasperini 



one began. These periods can be briefly out- 

 lined as follows: 



1. Causation of disease. This period began 

 in 1875 and continued to the end of the 19th 

 century. The predominant interest in the ac- 

 tinomycetes during these years was in their 

 role as pathogens, first in human and animal 

 diseases, especially actinomycosis in cattle, 

 and later in plant diseases, particularly po- 

 tato scab (R. Thaxter). 



2. Occurrence and importance in soil. Dur- 

 ing the next two decades, beginning about 

 1900, with the work of Beijerinck, and ending 

 about 1919, with the work of Krainsky, 

 Conn, and Waksman and Ciu'tis, the interest 

 in the actinomjxetes was predominantly 

 concerned Avith their occurrence in soils and 

 in other natural cin-iroiuneiits. The intro- 



duction of synthetic media ser\'ed to broaden 

 greatly our knowledge of the nature and oc- 

 currence of the actinomycetes. 



o. Biological period. Between 1919 and 

 1940, intensive knowledge accumulated con- 

 cerning the cultiu'al properties of the actino- 

 mycetes, their phj^siology, and their biochem- 

 ical activities, notably their antagonistic 

 effects upon bacteria and fungi. This period 

 may be said to haA-e begun with the work 

 of Waksman in 1919 and Lieske in 1921. It 

 continued with the studies of Gratia and his 

 group on the bacteriolj'tic effects of certain 

 actinomycetes and of Krassilnikov and his 

 associates on the antibacterial properties of 

 actinomycetes. l^roblems of \'ariability 

 (Schaal, Tempel, Kriss), decomposition of 

 plant and animal residues (Conn, Waksman 



