25 



103 



the acid formed by the lactic acid bacteria^), and we have thus now shown, on tlie other 

 hand, that the action of many lactic acid bacteria is furthered by the rennet. And in this 

 connection it should be mentioned that Barthel has recently shown-) how consider- 

 ably rennet increases the casein-splitting power in Slreplococcus laclir. The various 

 factors which give rise to the ripening of cheese thus mutually accele- 

 rate one another's action. Of other genuine proteins which may be utilised for the 

 cultivation of lactic acid bacteria, we may mention gluten and legumin dissolved in the 

 smallest possible quantity of sodium phosphate. This solvent may also well be employed 

 where casein is to be used in connection with other sugars than milk sugar. 



The most typical milk bacteria grow best in milk, and only with the greatest difli- 

 culty in peptone solutions; there are, however, lactic acid bacteria which, even though 

 they ferment milk sugar in peptone solutions, thrive poorly in milk, or require at any rate 

 to be accustomed to it, and which will in consequence rapidly lose the faculty of so doing 

 if left for many generations without coming in contact with milk at all. Indeed, it seems 

 possible to accustom the bacteria to largely dissimilar forms of nitrogenous nourishment, 

 and it is doubtless in many cases here that the main dilTereuce lies between the |)arasites 

 and the saprophytes most nearly related. The pathogenic forms have often so accu- 

 stomed themselves to a certain particular nitrogenous food (that from which their toxins 

 are also formed) that they can ill thrive without it. It has thus on the whole proved 

 considerably more difficult to keep the pathogenic streptococci alive than the sapro- 

 phytic. Many of the rod-shaped lactic acid bacteria of the digestive tract, also, were 

 tlifficult to cultivate, owing to the fact that we had not succeeded in satisfying their 

 |)articular requirements in respect of nitrogenous food. 



When seeking to compare the values of diiïerent nitrogen sources, the only possil)lc 

 method is that employed in agricultural chemistry, to wit, by offering the organisms the 

 same quantity of nitrogen in the different forms, but under conditions otherwise uniform. 

 In Table VIII will be found noted the quantities of acid (calculated, in the usual way, as 

 %o of the nutritive substrate) formed by some of our strains in horse scrum (S) Liebig's 

 meat extract (L), Cibil's do (Ci), Witte peptone (VV)^), casein peptone (C) and yeast extract 

 (Y), partly with the se|)arate sources alone, and partly when used with the addition of a 

 2% Witte peptone solution. It was so arranged that the quantity of nitrogen was through- 

 out 0.4%, 2 percent grape sugar was added, and the quantity of the different 

 nutritive salts was also kept as far as possible uniform throughout, save that no potassium 

 phosphate was added to the Wq. The last three columns of the table show the elTect of 

 this salt upon the casein pepton broth used by us, with 0.5% N. 



We had expected that the pathogenic bacteria would have preferred blood serum and 

 nieat extract, and the milk bacteria casein peptone. This however, did not prove to be the 

 case. The blood serum proved throughout a bad source of nitrogen, even 

 for pathogenic bacteria, and this despite the fact that its bactericidal substances 



') Landwirtschaftliches Jahrbuch der Schweiz. 1904, p. 404, and 1907, p. 97. 



-) Meddelande Nr. 171 från Centralanstalten for försöksväsendet på Jordbruksområdet. 1918 



3) The serum contained 1.13 »(o N, Liebig s Meat Extract 9.22 "l„ N. and Cibil s do. 3.11o,.. S Equal 



quantities of nitrogen from the two meat extracts had very nearly the same effect upon most of flic 



bacteria used. 



D, K. D Viilensk. Selsk. Ski-., naturvidensk. og malliem. Afd.. 8. Rickke. V. 2. 1* 



