W. A. Millard 161 



With the exception of No. 1 which was isolated in 1916, all the 

 cultures were isolated in August, 1918. Further examination of the 

 rAorphological and cultural characteristics of the cultures made it certain 

 that the organisms were members of the Actinomyces group, but, from 

 the first, considerable variations were observed between the 10 strains. 



An effort was made to compare them with the different species de- 

 scribed by Krainsky(6), Conn (7) and Waksman and Curtis (8), but in no 

 single case could complete agreement be found. This, however, is scarcely 

 surprising since, at the time when this work was being carried out, the 

 study of the Actinomycetes was so recent and the available literature 

 on the subject so scanty that the identification of species was supremely 

 difficult if not impossible. Moreover, it was soon discovered that the 

 characters of any culture underwent considerable variation with age, 

 conditions of growth and with extremely slight differences in the com- 

 position and reaction of the media on which they were grown. 



Since this time valuable contributions have been made to the subject, 

 on the morphological side by Drechsler(i8), and on the cultural side by 

 Waksman (19). The latter, in particular, has now placed the work of 

 distinguishing species on a sound basis by using only media of definite 

 chemical composition and degree of acidity throughout his cultures. 



A number of species are thus now clearly defined, but in the case of 

 Actinomyces scabies this is still by no means the case. 



Thaxter's (2) excellent description was of necessity incomplete. Lutman 

 and Cunningham (11) found what they considered "minor" differences 

 between various strains which they isolated, and, as before stated, placed 

 these strains in the species A. chromogenus (Gasperini). 



Finally, Waksman (19) in 1919 described a type of A. scabies based 

 on his own isolations of the organism but admits that a number of 

 cultures received from other investigators differ very considerably from 

 his own. 



In view of this apparent variation in the species or group species, 

 as the case may be, the writer felt no difficulty in considering the 10 strains 

 isolated by Miss Sampson as true A. scabies, provided their patho- 

 genicity to potatoes could be proved. 



Inoculation Experiments. 



These were carried out in unglazed pots 14 ins. in diameter, which 

 were filled with soil to within 2 ins. of the top and sterilised in the auto- 

 clave at 130° C. for 1 hour. Under these conditions it was found that 

 the temperature of the soil interior was raised to just over 100° C, which 



