VAKIATIONS. Ml'TATIOXS. WD AI ).\1TATI()X.S 



97 



concepts of \hv pleomorphists showed ;i 

 conAplotc lack of systematic in\'(»stijj;a1ioii. 

 Ill an attenij)! to patch together th(> lilc 

 cycles from haphazard obscix atioiis of cul- 

 tures in widely difTereut media, no considera- 

 tion was ji;iven to the age of the culture or to 

 the phase of growth. The designation of all 

 the structures by names borrowed in part 

 from mycology, in part from cytology, or 

 coined for the occasion serA-ed only to ob- 

 scure the problem and to make it more diffi- 

 cult for the reader to follow. Henrici empha- 

 sized that the necessity for creating a new 

 terminology had its origin in the oliscurity 

 of the thought which the author was trying 

 to express. The confusion introduced by this 

 terminology was all the greater because the 

 same structures were referred to by the 

 various authors under different names, and 

 the same names were used to designate differ- 

 ent structures. Henrici demonstrated experi- 

 mentallj^ that bacteria vary continually in 

 morphology with increasing age of the cul- 

 ture. He correlated morphologic variations 

 with the rate of growth, and showed that the 

 transition from one type to another occurs 

 at the points of inflection between phases of 

 the growth curve. 



Variations Among Microorganisms 



Among the major factors that influence 

 variability of microorganisms are: (a) the 

 previous history of the culture, (b) the na- 

 ture of the substrate or nutritional condi- 

 tions, and (c) the environmental factors. 

 Different organisms differ in this respect: 

 some species greatly resist \-ariation, others 

 readily undergo variation. 



One must differentiate between gradual 

 variation of an organism growing in a cer- 

 tain medium and mutation of the organism 

 that consists in a complete change of one or 

 more characters. Mutations are represented 

 by the appearance or disappearance of cer- 

 tain morphological or physiological prop- 

 erties, including production of pigment, 



foiinat ion of specific enzymes, power to cause 

 infect ion, jjroduct ion of aerial ni\'ccliinii, and 

 maimer of sponilal ioii. 



Some of the variations obtained for cer- 

 tain organisms may be permanent in nature; 

 others are only temporary. When a culture 

 is so treated as to result in injurious or 

 stinuilating effects, some of its properties 

 may be lost, whereas others may be gained. 

 Certain characteristics of the culture may not 

 change as a whole, but undergo only a degree 

 of change, as in the formation of adaptive 

 enzymes. Such variations are usually (juanti- 

 tative rather than (lualitative in nature. 

 When a comparison was made of the prop- 

 erties of a number of strains of S. griseus, 

 whether isolated from different substrates or 

 obtained from a single culture, all degrees of 

 gradation were obtained. These variations 

 involved the ability of the strains to produce 

 antibiotics or enzymes, the intensity and 

 nature of soluble and insoluble pigments, 

 and the length of the aerial hyphae. 



The effect of temperature upon the be- 

 havior of a given culture is illustrative. It is 

 sufficient to cite the classical observations of 

 Pasteur concerning a change in patho- 

 genicity of the anthrax organism when culti- 

 vated at 42°C, and the loss by Serratia 

 grown at 37 °C of its power to produce its 

 characteristic pigment. Other illustrations 

 comprise the increased power of infection 

 brought about by the reisolation of an or- 

 ganism from animal tissues infected with it. 



Variations among microorganisms include 

 the following: 



1. Xonhereditary modifications brought 

 about by the uncMjual influence of different 

 conditions. 



2. Hereditary continuous variations, char- 

 acterized by the gradualness of the change 

 through successive generations. These in- 

 clude (a) adaptive variations, in which the 

 nature and direction of the change bear an 

 adaptive relationship to the conditions under 

 which the change appears, (b) nonadaptive 



