BACTERIAL ACTIVITY 177 



are Jiberated only after the death of the bacteria, by the 

 breaking up of their bodies, and even then they cannot 

 be obtained apart from the bacterial protoplasm. Their 

 action has therefore been mostly studied by injection of 

 the dead bodies of bacteria. The effects produced are 

 not specific, but are more those of general disturbances 

 of metabolism ; nor does much time elapse before the 

 appearance of the symptoms, that is, there is no so-called 

 incubation time. 



The intracellular toxins are less sensitive to heat than 

 the soluble ones, but are mostly destroyed by heating to 

 70 C. The notable exceptions to this are those of the 

 tubercle bacillus, which are still toxic after digestion at 

 ioo C, and those of the B. enteritidis (Gaertner) which 

 remain toxic after the infected flesh has been cooked. 



Some organisms, such as B. anthracis, possess no soluble 

 toxin, nor does the injection of the dead bodies induce 

 toxic effects. Yet in the disease produced by the living 

 bacterium, symptoms which suggest toxin action are 

 present. To meet such cases, the hypothesis has been 

 made that these organisms only produce toxins in the 

 animal tissues, or may produce complementary substances 

 which assist the action of endotoxins. Such substances 

 have been studied under the name of " aggressins." An 

 animal is given a lethal dose of an organism, injected into 

 a serous cavity, into which a serous exudation results. On 

 the death of the animal, some of the exudate is taken, 

 most of the bacteria are removed by centrifugalizing, and 

 the few that remain by shaking up with toluol, and allowing 

 to stand for some days. This fluid, on injection, is non- 

 pathogenic, but has the power of increasing the effect 

 of the particular bacterium which has caused its production, 

 so that a non-lethal dose of the bacterium becomes a 

 lethal one ; and not only so, but the fatal effect is more 

 quickly produced. These results are ascribed to a 

 paralysing action of the " aggressins " on the phagocytic 

 functions of the leucocytes. Leucocidin, a true soluble 

 toxin produced by some strains of staphylococcus, causes 

 the death and partial solution of the leucocytes, and this 

 would suggest that the aggressins might after all be toxins, 

 either of the extra- or intra-cellular variety. 



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