198 H. JOEL CONN 



Actinomycetes in soil is not correct. With his special media 

 he claims to have found as many as 20,000 per gram of soil; 

 but he overlooks the fact that Hiltner and Stormer (1903) found 

 as many as 2.5 millions per gram. Moreover, in the work that 

 forms the basis of the present paper, 2 or 3 milHon per gram has 

 proved to be a very common figure; while on certain occasions 

 the number has reached 12 to 14 milUons. Occasionally over 

 half the colonies developing on gelatin have been Actinomycetes 

 — this in spite of the fact that Krainsky claims their growth 

 to be suppressed by ordinary media. 



The great abundance of Actinomycetes in soil has led to many 

 speculations as to their significance. It has often been stated 

 that they are active agents in the decomposition of organic 

 matter; but their part in this process has not been definitely 

 studied. Beijerinck (1900) showed that one type was often 

 present in the corky layer of various roots. He called this type 

 Streptothrix chromogena after Gasperini (1894) (who, however, 

 had called it Actinomyces chromogenus) . This type is one of 

 the most numerous in soil; yet in the fight of recent work it 

 must be regarded as a group rather than a species. To this group 

 belongs the causal organism of potato scab. Lutman and Cun- 

 ningham (1914), indeed, have recently attempted to show that 

 the cause of this disease must be renamed Actinomyces chromo- 

 genus because it agrees in every particular with Gasperini's 

 description of that organism. This is plainly impossible; for 

 Krainsky (1914) has shown that at least four separate species 

 agree with the descriptions that have been given to A. chromo- 

 genus. 



This fact brought out by Krainsky is very evident to anyone 

 who uses his methods for studying the group. In fact it has 

 proved possible, by the use of other special media^ besides those 

 described by him, to recognize many more types than those 

 listed in his article. Work is now in progress along this fine. 



- The medium which has given the best results of any yet investigated con- 

 tains: 1000 cc. water, 15 g. agar, 10 g. glycerin, 1 g. sodium asparaginate, 1 g. 

 glucose, 1.5 g. NH4H2PO4, 0.2 g., MgSOi, 0.1 g. CaCU, 0.1 g. KCl, trace FeCU, 

 Further media are now being tested out that may prove even more satisfactory. 



