474 PATHOGENIC MICROORGANISMS 



regarded as not a primary invasion, but as one associated with and 

 made possible by either traumatic injury or the co-operation of other 

 invasive germs such as streptococci, staphylococci and others. There 

 may, of course, in addition to these be rare instances in which the 

 Welch bacillus, owing to excessive virulence of the strain or relatively 

 low resistance of the infected individual, becomes the primary invader. 

 It is easy to understand under these conditions why severe trauma 

 associated with the carrying of soil would form ideal conditions for the 

 production of Welch bacillus infections. 



The most interesting chapter in the pathogenicity of the Welch 

 bacillus is its relation to intestinal disease. Simmonds confirms by his 

 own work the work of many others that the Welch bacillus may be 

 regarded as a normal inhabitant of the intestines of man. In 19 babies 

 under one year of age he found Welch bacilli in the stools of 8. He 

 points out that it has been found even in nursing infants by a number 

 of investigators. 



Herter 1 has associated the presence of the Welch bacillus in the 

 bowel with pernicious anaemia. However, no such relationship can at 

 present be assumed on the basis -of available work. 



Isolation. The bacillus may, of course, be isolated by anaerobic 

 plating methods. It is best isolated, however, from mixed cultures by 

 animal inoculation. If, for instance, it is desired to obtain it from a 

 mixed culture or from feces, a suspension of about 1 c.c. of the sus- 

 pected material is made in 5 c.c. of sterile. salt solution. This is thor- 

 oughly emulsified and filtered through a sterile paper. One to two c.c. 

 of this suspension is then injected into the ear vein .of a rabbit. After 

 four or five minutes the rabbit is killed. It is then placed in the incu- 

 bator for five to eight hours. At the end of this time, the animal is 

 usually found tensely distended with gas. At autopsy, gas bubbles 

 will be found distributed throughout the organs, most characteristically 

 in the liver, where isolated bubbles are found covering the surface. 

 From these bubbles cultures or smears may be taken for identification. 

 Identification is easily made from its morphology, its capsule, lack of 

 motility, and gas formation. 



The interest of bacteriologists in the Welch bacillus has lately 

 been attracted particularly by the frequent occurrence of the co-called 

 gas bacillus infections in soldiers in the trenches. Apparently, these 

 infections are due to the fact that dirty clothing and dirt from the skin 



1 Herter, "Bacterial Infection of the Intestinal Tract," New York, Macmillan, 1907. 



