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coccus is produced, which forms no slime at all. I the material for the re-ino- 

 culation is secured from the depth of the cultures grown in closed flasks, at 

 places where the access of air is impossible, and the inoculation is repeated once 

 or more in the same way, a Lactococcus is likewise obtained which displays no 

 trace of slime production. 



At some depht beneath the surface, however, is a zone in which unchanged, 

 slime forming, hereditarily constant material is found. 



What in this case can be very easily ascertained, proves, at accurate investig- 

 ation, also to be true for the other species of lactic acid ferments, namely, that 

 they only then continue to display constant specific characters, when they are 

 continuously cultivated at a certain pressure of the oxygen, else, these characters 

 are seen to disappear, whilst in fact, or apparently, news ones originate. Hence, 

 in some cases it may be proved, in others the probability is shown, that each 

 species must occur in three varieties, joined by intermediate forms, i.e. the normal 

 form, a high pressure variant*, and a low pressure variant. 



As in wholly different groups of bacteria corresponding facts may be ob- 

 served, there is cause to assign a fundamental signification to them. 



A decisive factor which may cause the production of variants is furthermore 

 the temperature, fox experience proves that a prolonged cultivation above the 

 optimum temperature of growth, gives rise to the appearance of forms distinctly 

 different from the original stock. 



In other cases the cause of the variability is unknown; not seldom for 

 example, we find at the very first culture of a species taken from nature, strongly 

 varying colonies, which prove to belong to the same species only because many 

 colonies by sector-variation display the genetic alliance ot the variants to the 

 wild stock. 



But then, too, there is reason to admit that the new vital conditions, to 

 which the microbes are subjected just by the change of oxygen pressure and 

 temperature, are the chief factors of the variation process which is, as it were, 

 seen in action. This observation is of so general a nature and is so closely related 

 to the essence of life, that it must be considered as probable, that also in higher 

 plants and animals, local changes in the access or exclusion of oxygen, in con- 

 nexion with temperature, play an important part in the morphogenesis. 



As the examination of other species of microbes shows that the absence of 

 certain nutrient substances in the culture medium, at free aeration and during 

 growth, may cause hereditary variation, for example in Schizosaccharomyces octo- 

 sporus, which in old cultures changes into the spore-free variant, totally differing 

 from the chief form, there is reason also to believe, that also the said factor 

 must be considered to explain the great variability of the lactic acid ferments; 

 but the observations there about are not vet fit for definite conclusions. 



3. Elective culture of the microbes of the slim\ lactic acid fermentation. 



There is reason to assume that the slime producing lactic acid ferments are 

 the normal forms and the non-slime formers, species or variants derived from 

 them. Hence, the former deserve to be considered in the first place. 



