sum 



EXPERIMENTAL INOCULATION 247 



summarized by saying that only once has a true diphtheria bacillus been isolated 

 from an animal spontaneously infected. The disease must therefore be exceedingly 

 uncommon among the lower animals, and statements to the effect that a case has 

 been observed, or an outbreak of diphtheria traced to infection from the lower 

 animals, should not be accepted without rigorous investigation.] 



3. In the circumambient media. 



The diphtheria bacillus is able to live outside the human body. Park, Wright and 

 Emerson found the organism in the dust of diphtheria wards and on the clothes of 

 the attendants. Abel also found it on the toys with which children infected with 

 diphtheria had been playing. 



Bacillus pseudo-diphtherise. 



The pseudo-diphtheria or Hofmann's bacillus, an organism in some respects closely 

 resembling the diphtheria bacillus but differing from it in being shorter and non- 

 pathogenic to laboratory animals and in other particulars, is fairly frequently met 

 with in the mouths of healthy persons. 



Reference is again made to this organism later in the present chapter (p. 273). 



SECTION I. EXPERIMENTAL INOCULATION. 



1. Symptoms and lesions produced in animals susceptible 



to infection. 



(a) Guinea-pigs. 



The guinea-pig is the most suitable animal for the study of experimental 

 diphtheria. The organism may be introduced either under the skin, into 

 the peritoneal cavity, into the trachea or on to mucous surfaces. 



1. Sub-cutaneous inoculation. 0'5 c.c. of a twenty-four-hour broth culture 

 inoculated sub-cutaneously will kill the animal in 24r-72 hours according to 

 the virulence of the organism. Following the inoculation there is a slight 

 oedema at the site of inoculation and a rise of temperature ; the animal shows 

 symptoms of illness and finally dies. 



If only a slightly virulent culture be used, the animal may recover ; in 

 that case there is some oedema at the site of inoculation, followed by a slough 

 which heals in course of time. [Similar effects result from the inoculation of 

 sub-lethal doses of fully virulent cultures.] In the oedema at the site of 

 inoculation the bacilli multiply for the first 6 or 8 hours following the inocula- 

 tion, after which multiplication ceases and their numbers decrease so that 

 post mortem relatively few organisms are found in the clear oedematous fluid. 



The organisms do not pass into the blood and internal organs. Post 

 mortem, there is a very marked congestion of the internal organs and especially 

 of the supra-renal capsules, and a large pleural effusion. The fluid is occa- 

 sionally blood-stained : it contains no bacilli. 



2. Intra-peritoneal inoculation. The symptoms following intra-peritoneal 

 inoculation are less severe than after sub-cutaneous inoculation : death is 

 longer delayed and does not occur till between the fourth and the twelfth 

 day. Over and above the ordinary visceral lesions there is an effusion of 

 fluid into the peritoneal cavity and it is only in this situation that bacilli 

 can be found. 



3. Intra-tracheal inoculation. Tracheotomy is first performed ; the 

 tracheal mucous membrane is then abraded and a portion of a culture of 

 diphtheria bacilli applied. A false membrane forms on the abraded surface 

 which sets up a true condition of croup rapidly followed by death. An 

 essential condition of success is that the mucous membrane be traumatized ; 

 the bacilli fail to develop on the uninjured membrane. 



