SYNOPSIS xi 



CHAPTER V 



VARIATIONS IN FERMENTING POWER 



The fermentation op carbohydrates— its stages. Different types of 

 variation. I. Different strains may possess different fermenting properties. 

 II. Tlie same strain may vary spontaneously. III. Fermenting properties 

 modified by conditions of growth. 1. Temperature. 2. Oxygen. 3. Atmo- 

 spheric pressure. 4. Age of culture. 5. Age of medium. 6. Composition 

 of medium — ^effect of carbolic acid, sodium benzoate, monochloracetic acid. 

 7. Influence of source — milk, urine, ascitic fluid. IV. Symbiosis. V. In 

 "carriers." VI. After "passage." VII. In disease. VIII. Prolonged con- 

 tact with a particular sugar. IX. Artificial selection — method often in- 

 effective. 



The significance of variations in sugar reactions. 1. Fermentation 

 due to enzymes which are destroyed by antiseptics. 2. Distinct enzyme for 

 each different sugar. 3. Different enzyme for each different stage in fer- 

 mentation. 4. Distinct enzyme for forming each acid. 5. Distinct enzyme 

 for producing gas from each acid. 6. New fermenting power an adaptation 

 to environment. 7. Such adaptation advantageous to organism. 8. En- 

 couraged by natural selection. 9. Explanation of incubation period — oc- 

 cupied by preparatory changes ? — this disproved, — interval before variation 

 appears? — this disproved, — time required for variants to predominate? — 

 does not explain definite length of period. 10. Reason for shortening of 

 period by subculture — subculture hastens reproduction. 11. Artificial 

 selection. 12. Reversion. 13, Variations apparently spontaneous — possibly 

 due to contamination of medium — or to impure sugar. No explanation of 

 spontaneous variation. 



The VAiuE of the sugar reactions — unsatisfactory as tests. 1. Time 

 allowance not fixed. 2. Reactions vary with temperature and other con- 

 ditions. 3. Media often unreliable — sugars impure — altered by sterilisation 

 — contaminated by glass vessel — deteriorate on keeping — acid reaction 

 masked. 4. Tests inconstant. 5. Positive or negative reaction a matter of 

 degree only. 6. Different carbohydrate groups yield different classification 

 — if designed to correspond with other tests useful for identification only. 

 Comparison between fermentation and agglutination tests — fermentation 

 tests may vary while agglutination constant — fermentation and agglutination 

 properties may both be altered — they yield a different classification — two 

 tests not related but may supplement each other. 



The value of variations in the sugar reactions in the identifica- 

 tion OF BACTERIA — Variations themselves constitute a test — may be specific 

 (cf. morphology of B. diph.) — ipay identify source of strain. (50 — ^70) 



