132 



54 



(Kruse). As will be seen, this bacterium has been regarded alternately as a rod form and 

 as a spherical form, which is due to the fact that its cells are often — as are indeed those 

 of most streptococci — somewhat loiigcr than they are broad. As the earlier descriptions 

 apply in reality to the entire genus Streptococcus (and largely also to that of Belacoccus). 

 none of the names suggested can claim priority. I believe, however, that it will be in con- 

 formity with even the strictest requirements in this respect to use the name Streptococcus 

 lactis, since the generic term Bacterium cannot be employed in the present instance. 



Streptococcus lactis is killed at a temperature of 60° — 70°. Its optimal temperature is 

 30°, but it can form just as much acid at 20°. It grows poorly as a rule below 10° or over 

 40°. In the case of several strains, the maximal temperature is reached already at 38°. 

 No. 16 grows at 42i/^°, and Nos. 13 and 14 even at 45°. 



Streptococcus lactis grows extremely fast under favourable conditions. When freshly 

 isolated from milk, it will coagulate sterile milk in less than 24 hours at 30°, forming therein 

 7 — S^/oo lactic acid. In this state it is also generally capable of dissolving a small quantity 

 of casein. This faculty is, however, in many strains, very soon lost, disappearing with 

 surprising rapidity when they are cultivated on artificial substrates, and they are then 

 but ill able to thrive at all in milk. The lost power can only rarely be restored by regular 

 transference from milk to milk. This feature, and the fact that many strains prefer maltose 

 to lactose, seems to suggest that milk is not the most natural substrate for the present 

 species. Possibly it may be derived from cowdung. It gives milk and cream either a purely 

 acid taste or an unpleasant flavour. 



Streptococcus lactis is characterised by its lack of, or extremely slight power to ferment 

 cane sugar. It is likewise incapable of fermenting raffinose, inulin, or (with the exception of 

 No. 1) starch, but does ferment dextrin and salicin. Like most other lactic acid bacteria, 

 it prefers lævulose, glucose and mannose to galactose. Of alcohols, it only ferments man- 

 nite, and not all strains can even ferment this. Its action with regard to pentoses varies. 

 Some strains ferment neither arabinose nor xylose (0-forms); others ferment one of these 

 pentoses, and others again both {A + X-forms). In Sc. lactis, as in most other lactic acid 

 bacteria, the power of fermenting one or another pentose is generally impaired or alto- 

 gether lost in the course of years: this faculty therefore is not suitable for further subdi- 

 vision of the species; we must as a rule restrict ourselves to noting under each species 

 0-forms, A -forms, X-forms and A + X-forms. In its relation to other sugars. Sc. lactis varies 

 only very rarely, but may do so at times, and we may in this respect call attention to the 

 interesting case of No. 12. This strain very soon lost the power of forming acid in milk. 

 Later on, it also lost the power of fermenting galactose, and naturally enough, the fermen- 

 tation of lactose in broth was reduced at the same time. 



At 20° — 30°, Sc. lactis (PI. I — IV) appears as a diplococcus, or in very short chains. 

 In milk, it is almost exclusively a diplococcus often slightly pointed. On agar streaks, 

 it may be elongated and markedly pointed. On A(î it now and again forms long chains. 

 At 10°, it always forms long chains, both in broth and on agar streak. .\t maximal tempe- 

 rature, it either forms long chains of cells having the normal appearance, or short chains 

 of irregularly swollen cells. 



Streptococcus crcmoris (Table XV). I have thus named tiie lactic acid bacteria 

 first studied by Storch, which, owing to its aroma formation, has become generally used 



