77 



155 



portions separately, the first generation Will be white and coloured respectively, but in 

 later generations, the t"wo Will as a rule again grow more alike. A Citreus-iorm from Krai, 

 which, like most of the other pure yellow micrococci, does not ferment sugar, was one 

 day found to exhibit yellow centre and White margin; the forms isolated from centre and 

 margin respectively retained their individual colours, pure yellow and pure white, for 

 four years, but were in all other respects entirely alike. In the fifth year, the white variety 

 turned pink. 



The size of tetracocci is highly variable. Strains Which appeared gigantic on isolation 

 had in the course of a few generations come down to the usual size. 



Spores were not observed in any of our strains. Nor did we succeed, by direct obser- 

 vation, in discerning any motility. Nevertheless, we must suppose that the most aerobic 

 forms (the A/ftus-forms, the mycodermalike as well as those which do not ferment sugar) 

 are capable of moving from a spot as, in old agar stab cultures, we constantly find isolated 

 colonies under the surface or at several mm. distance from the stab. 



None of our strains could stand any great quantity of ammonia, and they are there- 

 fore not able to effect any considerable fermentation of urea. The greatest transformation 

 of urea was effected by the Aureus- and Albus-îovms, and by the interniediate dung bac- 

 teria. On the other hand, most of our sugar-fermenting strains can rrdiici' nitrate to nitrite, 

 (the non-sugar-fermenting Cf/reus-forms lacked this power) thus differing from the strep- 

 to- and betacocci. Though nitrate reduction appears to be a constant quality, it is never- 

 theless not always to be used as a sj)ecies character. True, it agrees very nicely when 

 •we find that neither of the two closely related strains. Nos. 1 and 2, nor either of the two 

 identical strains. Nos. 30 and 31, are able to reduce nitrate, but the agreement is no longer 

 maintained when We come to consider the two strains. Nos. 3 and 4, which are eiitirely 

 alike save for the single fact that one of them reduces nitrate and the other not. It would 

 be unnatural to count them as distinct species on that account.. 



The tetracocci usually liquefy AG, though as a rule but slowly, often, indeed, only 

 after several weeks at 20°. The rapidly liquefying forms also liquefy SG, albeit somewhat 

 more slowly. Nos. 30 and 31, which are otherwise slightly liquefying, liquefy SG a little 

 faster than AG. Only strains which liquefy SG strongly (Nos. 9—13) attack the casein 

 of milk to any considerable degree. Exceptions are, however, Nos. 3 and 4, but they are 

 not able to break down the dissolved casein any further. 



The pathogenic tetracocci (the two Aureus- and Albus-îovms,) are killed already at 

 65°; most of our other strains, however, can stand a considerable length of time at 70° 

 or even 75°. The pathogenic forms grow at 45° ; but the maximal temperature for the re- 

 maining forms is rarely much above 40°, and often only 37V2°- The optimal temperature 

 is 30°, and the minimal rarely much below 15°, though the growth may still be rapid at 

 ordinary indoor temperature. 



The tetracocci can stand high concentrations of sugar and salt, though as a rule they 

 thrive better in Weaker concentrations. No. 1, which was isolated from anchovy pickle 

 With 15 7o NaCl, grows most rapidly with 57o NaCl. The power possessed by the tetracocci 

 of forming acid in sugar solutions with 10—15% common salt (See Table XI b) can as a 

 matter of fact be used as a specific character for them. As the tetracocci can stand both 

 heat, and high concentrations in the nutritive substrate, it is not strange that they should 



