THE COLON BACILLUS GROUP 239 



latter soon die out. (Typhoid bacilli usually die out in the filtrate of 

 colon culture.) Colon varieties differ as to whether they increase or 

 not in the old culture fluids of other broth colon cultures. The colon 

 bacilli act antagonistically to many of the proteolytic bacteria in the 

 intestinal tract, and so inhibit alkaline putrefaction by them. In milk 

 the same antagonism exists, probably because of the acidity caused 

 by the colon growth. 



Reaction to Temperature. Growth takes place best at 37 C.; the 

 range is from 5 to 45 C. Colon bacilli are killed at 60 C. in from 

 five to fifteen minutes. Frozen in ice a large proportion die, but some 

 resist for six months. In liquid air 95 per cent, are killed in two 

 hours. 



Resistance to Drying. The colon bacillus is quite resistant. Simple 

 drying destroys the majority of organisms dried at any one time, but 

 some bacilli of the number dried may remain alive, especially when 

 held in the texture of threads, for five to six months, or all may die in 

 forty-eight hours. 



Effect of Light. In water exposed to direct sunlight colon bacilli 

 are killed in from one to six hours. In diffuse light a moderate effect 

 only is produced. They are fairly resistant to Roentgen rays, quite 

 so to the electric current. 



Effect of Acids. The colon bacilli grow in a wider range of acids 

 and alkalies than most other bacteria. They develop in from 0.2 to 0.4 

 per cent, of mineral acids in from 0.3 to 0.45 per cent, of vegetable 

 acids, and in from 0.1 to 0.2 per cent, of alkalies. 



To most antiseptics they are resistant, growing feebly even in 1 : 5000 

 formaldehyde. They grow in from 6 to 8 per cent, of salt and live in 

 concentrated solutions. 



Effect of Animal Fluids and Juices. Gastric juice kills colon bacilli 

 when not protected or too greatly diluted by food. They grow in bile 

 and in the intestinal juices. Fresh rabbit and dog blood kills colon 

 bacilli, as also but more quickly typhoid bacilli. Calf and horse serum 

 are said to be inactive. 



Virulence of Colon Bacilli. Pathogenic Properties in Animals. The 

 virulence varies with the culture and the time since its recovery from 

 the intestines. Other things being equal, it is more virulent from an 

 intestinal inflammation. From severe diarrhoea the colon bacilli in 

 0.25 c.c. bouillon culture may kill guinea-pigs if given intraperitoneally, 

 while from healthy bowel 2.5 c.c. are usually required. Smaller amounts 

 are fatal to white mice. 



INCREASE OF VIRULENCE OUTSIDE THE BODY. It has been found 

 by several observers that in fermenting fecal matter a marked increased 

 virulence takes place, so that infection is produced when received by 

 man. Some investigators claim that by growing the colon bacilli with 

 typhoid bacilli and with the pyogenic cocci increase of virulence occurs. 

 This is improbable outside the body. The lesions following injection 

 with colon bacilli do not differ from those produced by the typhoid 

 bacilli. 



