EXPERIMENT STATION BULLETINS. 461 



Fenncntation in Verij Yoiiiuj Cultures. — Tlie second point requiring 

 ;ni explanation is tlie assumption that bacteria cause fermentation as 

 soon as they are transferred into a suitable medium. This assumption 

 contradicts the opinion of many bacteriologists who believe that bacteria 

 do not begin to ferment until a certain period of growth has been reached. 

 It seems a rather general belief that microorganisms in the earliest 

 stage of growth do nothing but multiply and after they have reached 

 a certain number, fermentation starts in and multiplication becomes 

 slower, AVhen and where this idea originated can not be ascertained, 

 but the general opinion is inclined to separate the tw^o processes as 

 independent. Two quotations will suffice as examples: Knosel (Cen- 

 tralbl. f. Bakt. II, Bd. 8, p. 272) speaking of multiplication and fer- 

 mentation of yeasts, says: "Both these life functions run parallel; as 

 a rule, however, esi)ecially with a small inoculation of yeast, the sugar- 

 destroying action is preceded by a short multiplication. After this 

 has taken place, fermentation begins." 



H. W. Conn (Bacteria in :\ri]k and Its Products, 1903, p. 74) states: 

 ''Now, while there is a general parallelism between the growth of these 

 organisms and the i)roduction of lactic acid, the parallel is by no 

 means a close one. For a considerable time after milk is inoculated 

 with lactic bacteria, there is no increase in the amount of lactic acid, 

 although the bacteria are themselves multiplying rapidly and becoming- 

 very numerous. Then there is a rapid increase in the development of 

 lactic acid, accompanying a still further growth in the bacteria." 



These quotations are just chosen to illustrate the general opinion of 

 bacteriologists. No data are on record to prove the above statement 

 that in the earlier stages of growth, multiplication goes on without or 

 with but little fermentation. In fact, no data can exist because it is 

 impossible to prove either contention. It requires but a very simple 

 computation, to show the impossibility of any proof. Sour milk with 

 about 1% of lactic acid contains at least 1,000,000,000 bacteria per cc. 

 If it takes 1,000,000,000 bacteria per cc. to make 1% of lactic acid, 

 1,000.000 bacteria would make 0.001% of acid in the same time, which 

 is much less than can be determined analytically. It would also take 

 1,000,000 bacteria one thousand times as long' to make 1% of lactic acid. 



This is the point that is commonly overlooked. A few thousand 

 bacteria are inoculated into milk, they multiply rapidly, after a few 

 hours, there are several million cells per cc, and yet no acid; the con- 

 clusion is that they did not form any acid in this period. This de- 

 duction is wrong. A calculation will show that if thev form acid at 

 the ordinary rate, the amount cannot possibly be detected by the usual 

 chemical methods. This explains also the fact that the discrepancy be- 

 tween growth and fermentation is observed especially with small in- 

 ocula. With large inocula, the i)roducts appear soon after, and the 

 "parallelism" is proved. 



The definition "Period of incubation is the time during which bacterial 

 proliferation is taking place without a corresponding increase in acid- 

 ity" is not based on actual data. From the time the products are 

 formed in quantities sufficient to be analyzed the parallelism is doubt- 

 less established. Why should a discontinuation of the parallelism! be 

 supposed as long as there are no indications of it, no present means of 

 establishing it. and no pertinent analogies even to make it appear 



