SCIENCE. 



[N. S. Vol. V. No. 130. 



the typical typlioid bacillus to represent 

 tlie types of this group that present the 

 greatest divergences in biological peculiari- 

 ties, we conclude, as others also have done, 

 that there is a series of closely related forms 

 that may be regarded as intermediate or 

 transitional, and which serve to establish 

 a biological relationship, either near or re- 

 mote, between these two typical members. 



From our own studies we are inclined to 

 regard the typical colon bacillus as the type 

 of this group, for the reason that its func- 

 tional equilibrium, as observed in the intes- 

 tine, is so permanent a quality that it may 

 readily be perpetuated under what is ordi- 

 narily regarded as favorable artificial cir- 

 cumstances, and that with the continuance 

 of such conditions there is no conspicuous 

 tendency on the part of this organism to 

 deviate from what we regard as its norm ; 

 whereas, on the other hand, with all the 

 other members of the group with which we 

 have worked there is not only a lack of 

 uniformity in the adjustment of the func- 

 tions, but such as exists is readily disturbed 

 under artificial environment, though it 

 must be borne in mind that even with the 

 typical colon bacillus we have also shown 

 functional modifications to be possible under 

 particular conditions. 



That when the members of the colon group 

 are cultivated under circumstances favor- 

 able to the development of both the func- 

 tion of fermentation and that of proteolysis, 

 fermentation invariably takes precedence 

 and no evidence of proteolysis is manifested 

 until after fermentation has ceased. 



That the cultivation of all the members 

 of the colon group under circumstances that 

 favor the development of one function, viz., 

 that of proteolysis, at the expense of 

 another, viz., that of fermentation, results 

 first in apparent increase of vigor ; but this 

 is of temporary duration and is quickly fol- 

 lowed by the decline and death of the cell. 



The result of this increased activity of 



the proteolytic function is the formation of 

 much larger amounts of indol by typical 

 colon cultures than has ever been obtained 

 by us by any other method. 



By the method of experimentation through 

 which we were enabled to accentuate the 

 proteolytic activity of the typical colon 

 bacillus, as caused by an increase of indol 

 formation, we have also induced the func- 

 tion of indol formation not only in atypical 

 colon bacilli that have been devoid of it 

 but in every specimen of typical typhoid 

 bacilli to which we had access as well. 



We feel justified in regarding one of the 

 differential tests between the typhoid and 

 colon bacillus, notably that of indol forma- 

 tion on the part of the latter and the ab- 

 sence of this function from the former, as 

 of questionable value, for the reason, as 

 shown above, that by particular methods of 

 cultivation indolproduction has been shown 

 to accompany the development of a number 

 of specimens that we have every reason to 

 regard as genuine typhoid bacilli. 



As a result of our own experiments, to- 

 gether with the observations of others, there 

 can be no doubt that the bacillus coli com- 

 munis at times possesses pathogenic proper- 

 ties, and that by artificial methods on 

 treatment it may often be brought from a 

 condition of benignity to one of virulence, 



The spleen of a typhoid patient has al- 

 ways been regarded as the only trustworthy 

 source from which to obtain the typical 

 typhoid bacillus. While we believe this to 

 be true, still our investigations show that 

 other members of the colon group may also 

 be present in this viscus ; in fact, ft-om such 

 spleens we have isolated practically all of 

 the varieties of this group with which we 

 are acquainted. 



From our experience the value of the 

 serum test for the differentiation of typhoid 

 and colon bacilli would seem to be ques- 

 tionable. We are inclined, however, to at- 

 tribute the irregularities recorded above as 



