Waksman — 4 — Actinomycetes 



4. It has now been established that we are dealing here, not with a 

 few species of a highly specialized and limited group of organisms, but 

 with a large and heterogeneous group comprising many thousands of 

 species which occur in numerous natural substrates and which take part 

 in many natural processes. Because of this, it has been generally felt 

 that a more comprehensive study of these organisms and the separation 

 of the group into several genera were justified. One of the main diffi- 

 culties, however, was the problem of digesting a most extensive litera- 

 ture. 



Until very recentlv, too little was known of the morphology and 

 physiolog}^ of the actinomycetes to justify recognition of basic differences 

 between the different forms in an attempt to establish specific types. 

 Most of the descriptions of the individual species were based largely 

 upon cultural characteristics, usually growth on media highly complex 

 in composition. Production of pigment in the mycelium of the organ- 

 ism and excretion of the pigment into the medium were considered 

 among the most important distinctive characters. The presence or ab- 

 sence of growth on certain media, the liquefaction of gelatin, the diges- 

 tion of milk proteins, and the production of odor were regarded as other 

 distinguishing features. Insufficient recognition was given to the fact 

 that these characteristics varied greatly under different conditions of cul- 

 tivation, such as composition of the medium, oxygen supply, and tem- 

 perature of incubation of the culture. The fact that an organism may 

 undergo various cultural changes when grown for some time on artificial 

 media was also disregarded. Certain aspects of the life cycle of a cul- 

 ture, such as the phenomenon of lysis and the problems of variation and 

 mutation, so common among these organisms, were not recognized at all. 



In the face of these shortcomings, the difficulty of establishing type 

 cultures is understandable. In most cases, it was much easier to desig- 

 nate any freshly isolated strain by a new name than to identify it with 

 a previouslv established species. Since the comparisons were usually 

 made not with type cultures but with written descriptions, which were 

 frequently -quite inadequate, the resulting confusion is not surprising. 

 Through the years, many new names accumulated, with the resulting 

 difficulty of recognizing the relations of the designated organisms to 

 older or previously described types. 



With all these limitations, however, information was gradually ac- 

 cumulating concerning proper methods of growing actinomycetes on 

 synthetic media. The specific morpholog)^ of different forms was be- 

 coming established. This helped in recognizing the true systematic 

 position of the group, and pointed to its separation into several distinct 

 and easily recognizable t)^es, which could be raised to the status of 

 genera. 



No attempt will be made to review in detail the early literature on 

 the actinomvcetes. Such reviews may be found in the monographs of 

 LiESKE (260), Orskov (328), Duch6 (98), Kriss (242), and Kras- 



