774 



SCIENCE. 



[N. S. YOL. IV. No. 100. 



Smitli as the typical colon bacillus, the 

 transitional forms of the colon bacillus, and 

 the pseudo forms of the colon and the ty- 

 phoid bacillus, having been furnished to 

 Dr. Billings, and placed in the hands of the 

 writer, these have been studied for the pur- 

 pose of becoming able to identify the differ- 

 ent members of the colon group met with in 

 further research, and an effort has also 

 been made to differentiate each species by 

 the appearance of its colonies. 



The colonies on gelatine plates were 

 drawn at different stages of growth and 

 compared as to variations in size, outline, 

 color and surface-markings ; but these dif- 

 ferences were not found to be greater than 

 have often been observed in the typical co- 

 lon bacillus grown in an unfavorable me- 

 dium, or at a low temperature, or under 

 some other unusual condition. The atyp- 

 ical forms of the colon bacillus, found in 

 water and sewage, may present changes in 

 microscopic appearance due to their envi- 

 ronment. Therefore this means has not 

 been found to be of much positive value in 

 determining a variety. 



Cultures of each variety were then ob- 

 served in an unfavorable medium. Bouillon 

 containing subnitrate of bismuth in vary- 

 ing amounts, one per cent., one-half per 

 cent., and one-tenth per cent., was first 

 used. The bismuth subnitrate was rapidly 

 reduced in the one-tenth solution ; and 

 more slowly in the others. After remain- 

 ing for twenty days in this medium the 

 colonies became irregular in shape, but this 

 feature was not more prominent in any one 

 variety than in another, and it is of con- 

 stant occurrence whenever the bacillus is 

 kept for a long time without change of me- 

 dium, or in distilled water. 



Salicylate of bismuth was also used in the 

 same manner. The same grotesqueness in 

 the shape of the colonies was observed in 

 the one-tenth per cent, solution, which was 

 the only one in which the cultures lived. 



A study of the different members of this 

 group in stroke cultures on the various 

 media in general use showed this means of 

 differentiation to be of less value than the 

 appearance of the colonies on gelatine 

 plates. On agar-agar the only variation 

 observed in the different types was, that in 

 some cultures the growth stained the me- 

 dium a yellowish-brown color while in oth- 

 ers no such staining occurred. On blood- 

 serum the growth was scanty in every in- 

 stance and there was a tendency to remain 

 in distinctly separate colonies. On gela- 

 tine, every variety presented a tufted ap- 

 pearance to some degree. A slight cloud- 

 ing of the gelatine around the growth was 

 seen in the most alkaline cultures. The 

 so-called artificial potato made of Peter- 

 mann's fluid, stiffened with rice powder, 

 potato-starch and calcined magnesia was 

 tried, but was found to be very unsatisfac- 

 tory, because of its constant alteration in 

 reaction, produced by the action of the acid 

 on the phosphates and carbonates, which 

 action continued until the composition of 

 the substance was entirely changed. 



The reaction of cultures of the colon ba- 

 cillus group as found by testing a consider- 

 able number of each different type, is al- 

 ways alkaline in media which do not con- 

 tain sugar. In sugar bouillon the reaction 

 varies with the kind of sugar used. If the 

 sugar is broken up by the ferment of the 

 organism, enough acid may be formed to 

 finally kill the culture, but if only a small 

 amount of acid is formed, then the culture 

 finally produces an alkaline reaction. 



The indol reaction was found of much 

 value in testing certain varieties of this 

 group. Some difficulty was experienced in 

 obtaining an accurate test in cultures in 

 which only a slight trace was present. 

 The well-known test as given by Kitasato 

 was used. Notwithstanding the great care 

 taken in testing, ten tests made upon each 

 organism gave greatly varying results. The 



