172 BIOLOGY OF PNEUMOCOCCUS 



In summary Rosenow wrote: 



The changes observed have frequently the characteristics of true mu- 

 tations because they appear suddenly, under conditions more or less ob- 

 scure and because the newly acquired properties persist unless the or- 

 ganisms are again placed under special conditions. A pre-mutational 

 stage seems to be necessary because the same strain will not yield mu- 

 tants when placed under what seem to be identical conditions at differ- 

 ent times. The underlying conditions which tend most to call forth 

 changes are, first, favorable conditions for luxuriant growth and then 

 unfavorable conditions — under stress and strain. This seems to call 

 forth new or latent energies which were previously not manifest and 

 which now have gained the ascendency and tend to persist. This may 

 hold true in vivo also. This fact makes it difficult to obtain mutations 

 outside of the body with highly virulent strains, because they die before 

 there is opportunity for the organisms to adjust themselves to the new 

 conditions. It explains why injection into cavities makes for greater 

 changes than intravenous injections of moderately virulent organisms. 

 Apparent mutations in animals have been observed almost exclusively in 

 closed cavities, such as joints and pericardium, and here mostly when 

 the tissues of the host were gradually getting the upper hand and the 

 organisms were being destroyed. The mutations in vitro may be spoken 

 of as "retrogressive" and those in animals as "progressive" because evi- 

 dences of a vigorous vegetative life are diminished whereas in the latter 

 they are usually increased. 



The results and conclusions of Rosenow have been transcribed in 

 some detail because they represented such a wide departure from 

 established belief. The announcement was greeted with much skep- 

 ticism. Such sudden and wide shifts from one to another suppos- 

 edly fixed species appeared to violate biological laws, and it seemed 

 that some artifact must have been responsible for the remarkable 

 transformations. Nowhere in the literature, with the exceptions to 

 be described, have references been found which duplicate or sub- 

 stantiate Rosenow's results. 



Wolff (1923), 1534 in a long theoretical discussion of pneumococ- 

 cal mutation, suggested that the members of the large tribe Strep- 

 tococcaceae, from pure saprophytes to true parasites, in spite of 



