Variations in Bacteria Caused by Change of Medium 3 



characteristic in the organism or in the colonies of the two plates. 

 In this experiment enough evidence is presented to assume that the 

 question of old age in this strain may be considered as eliminated. 



The laws of adaptation, on the other hand, govern the internal 

 state of the organism in its present conditions either fully or only 

 partially. If the organism is fully habituated to its environment, 

 a substantial change of environment effects a growth which is sparse; 

 or, really or apparently abundant; or, no growth at all. If the abun- 

 dant growth is apparent, and not real, it will be transitory; if real, 

 it will persist. 



Whether bacteria obey the laws of adaptation fully, partially, or 

 not at all, may or may not be proven by external phenomena; but 

 since the question should receive some answer from an examination 

 of internal protoplasmic conditions, a priori an organism confined to 

 one environment for many generations ought to offer help to this end. 

 The exact number of generations that will influence bacteria in this 

 direction has not been determined. Arbitrarily, therefore, the 200 th 

 generation was chosen to initiate the solution of the question. In 

 all the following experiments the organism has been confined to one 

 medium for at least 200 generations before it was finally grown on this 

 medium for examination. 



In order to determine the biological activity of the organism in its 

 present environment, it was cultured on medium to which it had been 

 accustomed, i.e., agar, 2.5 per cent; peptone, i.o per cent; NaCl, 

 0.5 per cent; meat-extract, i.o per cent; incubated in test tubes 

 8xi inch at 37 C. Under these conditions growth after 24 hours was 

 fairly abundant, and even seemed to increase after that period. 



To prove approximately an increase or decrease in growth after 

 24 hours' incubation, 100 tubes of different ages were selected, the 

 planted area of which seemed to be of the same dimension. The 

 growth was scraped from the medium at 24-hour intervals, transferred 

 to weighing bottles, and weighed. After weighing, the material was 

 carefully preserved at o to 5 C. for further examination. 



Growth of 9 to 1 1 days proved to be the maximum. 



In as much as the presence of moisture affects the weight of the 

 collected bacteria, it is necessary to determine what relation moisture 

 bears to the organism. This determination will decide whether, and 

 to what degree, the growth has been increased really or only apparently. 

 Determinations, therefore, of the water content were made by drying 



