78 



SCIENCE 



[N. S. Vol. XXXIX. No. 994 



is peculiarly qualified to be of service, in 

 striking sparks by the contact of experience 

 in the dififerent fields of bacteriology, and 

 in viewing all our special problems by the 

 clear light of fundamental biological prin- 

 ciples. 



The task of the biologist is the study of 

 the reactions of the group of allied sub- 

 stances we call protoplasms, under the in- 

 fluence of various physical and chemical 

 conditions of the environment. Instead of 

 the pure compounds of the chemist we must 

 deal with organisms, interacting mixtures 

 of substances, different for each kind and 

 even for each individual plant and animal. 

 In very refined work such as is involved 

 in the determination of reaction times by 

 the psychologist or in our own studies of 

 the action of disinfectants, even the per- 

 sonal equation of the individual or the in- 

 dividual strain must be taken into account. 

 For most purposes, however, the species or 

 kind of organism displays reasonably uni- 

 form characteristics, and may be used as 

 our pra,ctical unit of study. A clear dis- 

 tinction between the kinds of organisms 

 involved and a clear conception of the rela- 

 tion between these kinds is certainly how- 

 ever imperative, and a sound basis for the 

 characterization and classification of the 

 organisms with which we deal is one of the 

 most pressing needs of bacteriology. 



The fact that we have lacked in the past 

 any sound system of sorting out and ar- 

 ranging bacterial types requires no elabo- 

 rate demonstration. The question of what 

 constitutes a colon bacillus has agitated 

 sanitary bacteriologists for three decades 

 and is still unsolved. And to take a still 

 more striking and still more important case, 

 consider the controversy as to the Vielheit 

 or the Einheit of the streptococci, which 

 has raged so long. Here is a group of or- 

 ganisms, the part played by which in a wide 

 range of diverse diseases is found to be 

 more fundamental — a group which I am 



inclined to think produces in the aggregate 

 more suffering and death — than any other 

 group, except the acid-fast bacilli. Yet we 

 are almost wholly at sea in regard to their 

 identification and mutual relationships. 



There are two very distinct types of 

 variations characteristic of organisms in 

 general, fluctuations and mutations, and 

 both are well recognized among bacteria. 

 Fluctuations are the minor quantitative 

 differences which group themselves on a 

 curve of frequency when a large series of 

 individuals is studied, as a rule due to the 

 chance effects of environment and not in- 

 heritable. Thus, for example, Walker and 

 I (Winslow and Walker, 1909) found that 

 one hundred different subcultures of a sin- 

 gle strain of the paratyphoid bacillus race 

 A gave acidities in dextrose broth varying 

 between 1.1 and 1.6 per cent, normal, while 

 a similar series of lines of race B gave 

 acidities varying between 1.3 and 1.9 per 

 cent, normal. We took the subcultures of 

 each type giving maximum and minimum 

 acidities and isolated one hundred sec- 

 ondary subcultures of each. The curves 

 from these extreme cultures however in 

 spite of the diversity exhibited by their im- 

 mediate parent stock, went back to the 

 curves characteristic of their respective 

 races, with a mean value of 1.4 for race A 

 and of 1.6 for race B (Fig. 1). These 

 fluctuating variations are clearly of no sys- 

 tematic significance and must be eliminated 

 from consideration by a study of numerous 

 strains of the same type. 



It seems on the whole most convenient 

 to limit the term fiuctuations to such non- 

 inheritable variations as those just de- 

 scribed. At times, however, we find in our 

 cultures variations of apparently similar 

 nature, but distinguished by the fact that 

 selection among them does produce per- 

 manently different races. Thus, Goodman 

 (1908) carried out experiments with the 

 acid production of B. diphtherias somewhat 



