On different forms of hereditary variation of 



microbes. 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amster- 

 dam, Vol. Ill, 1900, biz. 352 365. Verscheen onder den titel Over verschillende 

 vormen van erfelijke variatie bij mikroben* in Verslagen Kon. Akademie van Weten- 

 schappen, Wis-en Natuurk. Afd., Amsterdam, Deel IX, 1900, biz. 310324, en onder den 

 titel Sur diverses formes de variation hereditaire chez les microbes* in Archives 

 Neerlandaises des Sciences Exactes et Naturelles, Haarlem, Serie II, Tome IV, 1901, 



p. 213230. 



The interesting lecture of Prof. Hugo de Vries in the last meeting of the 

 Academy on the origin of new forms in higher plants, induces me to draw 

 attention to some observations regarding the same subject in microbes. 



Though the culture of microbes, compared to that of higher plants and animals 

 is subject to many difficulties, it cannot be denied that, these once mastered, micro- 

 bes are an extremely useful material for the investigation of the laws of heredity and 

 variability. The starting from the single individual, which of course is required here, 

 is commonly almost as simple as for the higher organisms, and it is want of practice 

 only which makes it appear so troublesome. The generations succeed each other 

 quickly ; hundreds, nay thousands of individuals can be very easily surveyed in their 

 posterity; far remote classes of the natural system are represented by microbes; in 

 many the variability is great 1 ). Even the difficulty of determining the species and 

 varieties, which is frequently only possible by means of biochemical investigation, 

 can become an advantage, for the very reason that biochemical methods of distinction 

 are very accurate, can be extended in various directions and compared by measure- 

 ment. Thus the species and varieties of lactic-acid ferments are distinguished by 

 titration, alcohol ferments by means of the saccharometer, while different carbohy- 

 drates can be selected as the base of lactic-acid and alcohol fermentation. To all this 

 is added the circumstance that it is easy to perform with microbes experiments of 

 competion, which is difficult or impossible with higher plants and animals, and it is 

 well-known how delicate the distinctions are which are thereby revealed. 



In comparing the results obtained with microbes to the rules found in higher 

 organisms, account should be kept, first, with the want of sexuality, by which the 

 variation of microbes becomes comparable to the bud-variation of the higher plants, 

 and, second, with the unicellularity of the microbes. As to the first point the ex- 

 periences with the bud-variants of higher plants seem to prove that an essential dif- 

 ference between bud-variation and seed-variation does not exist. As to the uni- 



') Compare Rodet, De la variabilite dans les microbes, Paris 1894. Bibliography 

 wants in this book and not all data are trustworthy. 



