BIOLOGICAL PROPERTIES 361 



3. Toxin. 



(i) Filtered cultures of the dysentery bacillus are generally only slightly 

 toxic, and even in large doses merely cause a temporary loss of weight ; but 

 the blood of the inoculated animal acquires the property of agglutinating the 

 bacillus. Todd and Rosenthal however obtained a strong toxin, which was 

 fatal to rabbits in doses of 0'2 c.c. sub-cutaneously, by growing the bacillus 

 in Martin's broth at 37 C. for 3 weeks and then filtering. Their results have 

 been confirmed by Ludke and Doerr. , 



(ii) Unfiltered cultures of the dysentery bacillus killed by heat (58 C. for 

 1 hour or 85 C. for 30 minutes) or chloroform, when inoculated into rabbits 

 intra-peritoneally, intra-venously or sub-cutaneously, lead to a fatal result 

 similar to that produced by the living organism and accompanied by diarrhoea 

 and hypersemia of the mucous membranes of the colon (Drigalski and 

 Conradi). 



(iii) Endotoxin. Conradi, Neisser and Shiga, Vaillard and Dopter, and 

 Besredka have extracted an intra-cellular toxin from the bodies of the 

 bacilli. 



Conradi' s method. Scrape the growth from an agar culture and make into an 

 emulsion with normal saline solution. Place the emulsion in the incubator at 37 C. 

 and leave for about 30 hours, then decant the clear liquid, filter through a Berkefeld 

 bougie and finally evaporate in vacuo to one- tenth its original volume. 



2. Neisser and Shiga' s method. Heat an emulsion of bacilli in normal saline 

 solution to 60 C., allow to stand for 48 hours at 37 C. then filter through a Reichel 

 filter. 



3. Vaillard and Dopter' s method. Make a thick emulsion of bacilli from an agar 

 culture with sterile water, heat to 58 C. for an hour, distribute in tubes, seal in the 

 blow-pipe and leave in the warm (37 C.) incubator for a month. The clear super- 

 natant liquid is used without filtration. 



4. Besredka' s method. Besredka has applied his method of extracting endotoxin 

 (p. 379) to the dysentery group. The endotoxin is very toxic and kills rabbits in 

 doses of 0'05 c.c. 



The Shiga bacillus alone produces dysentery toxin, bacilli of the Flexner type 

 being almost invariably atoxic. 



c/ U 



Properties of dysentery toxin. The toxin kills dogs, rabbits and mice with 

 all the symptoms of a dysentery infection. The fatal dose for rabbits varies 

 according to the method of preparation and the method of inoculation (intra- 

 peritoneal. intra-venous or sub-cutaneous) from O05 c.c. (with Besredka's 

 endotoxin) to 2-5 c.c. Administered by the mouth it gives rise to no 

 symptoms. 



Dysentery toxin is less affected by heat than are many other toxins : it 

 is, for instance, unaltered by being exposed to 70 C. for an hour, but a tem- 

 perature of 75 C. weakens it and at 80 C. its properties are rapidly destroyed. 

 It is now admitted that dysentery toxin is not a soluble or diffusible toxin but 

 an endotoxin retained within the bodies of the bacilli. 



4. Vaccination. Serum therapy. 



(i) Shiga has shown that animals can be immunized by inoculating them 

 sub-cutaneously with small doses first of dead bacilli then of living bacilli. 

 The serum of immunized animals agglutinates the bacillus and. has both 

 prophylactic and curative properties. 



Small animals are very difficult to immunize and it is therefore better to 

 use a goat or an ass or an horse ; horses must be treated very carefully. 



The serums (ass and horse) obtained by Shiga and by Kruse protect guinea- 



