RESEARCHES ON ASPOROGENATION. 263 



intermediate, temporarily asporogenic forms appeared as soon as 

 the treatment commenced ; and since they were never found in 

 the original material, their origin must therefore be attributed to 

 the treatment applied. Finally, the variation in question is a 

 universal phenomenon, appearing in all cases when the cells are 

 subjected to the treatment described. The results obtained, both 

 from the analysis of the original material and that of the various 

 stages of the treatment, indicate clearly that the variation pro- 

 duced by the treatment is due to transformation or modification. 

 It has been urged against this view that, since all the cells are 

 of equal value, they must all undergo transformation at the same 

 time if the process is really one of modification. This, however, 

 is incorrect, since the cells are far from being of equal value, their 

 condition at the moment of commencing the treatment differing 

 considerably in respect of age, nutrition, &c., and therefore the 

 transformation cannot proceed simultaneously with all the indi- 

 viduals present. 



A highly characteristic feature, which was also tested experi- 

 mentally by Hansen, is that, even when the initial material 

 consists of a single vegetative cell or spore, the following three 

 classes : sporogenic cells, temporarily asporogenic cells, and con- 

 stantly asporogenic cells, appear during the treatment. From the 

 two former classes it is possible to take single cells which in turn 

 produce members of all three classes. This also proves the change 

 is due to modification, inasmuch as these intermediate forms, 

 which revert to the sporogenic form when excluded from the 

 treatment, become constantly asporogenic only after treatment 

 for a considerable time. 



With regard to the conditions necessary for the modification, 

 it might be thought that the chemical composition of the nutrient 

 medium, the vibration produced by shaking the flask, the aeration 

 of the medium, and the temperature would constitute influential 

 factors. The experiments, however, showed that neither vibra- 

 tion nor a medium of definite chemical composition is essential ; 

 and that aeration is incapable of bringing about the change in the 

 absence of the high temperature. The nutrient liquid, vibra- 

 tion, and aeration exercise an indirect influence, inasmuch as 

 they more or less facilitate reproduction, but the high tempera- 

 ture forms the most important and absolutely indispensable 

 factor. 



In the foregoing experiments Hansen used nutrient liquids for 

 the cultures, but he also tried solid media. In the latter case 

 several species produced constantly asporogenic cells when allowed 

 to remain on wort gelatin at 25 C., or at ordinary temperature, 

 and it may be assumed that chemical factors were -here in opera- 

 tion. When grown at 32 and 34 0. on wort-agar gelatin under 

 the same conditions as in the experiments with liquid media, i.e., 

 repeated re-inoculations at short intervals, Sacch. Pastorianus 



