164 THE TOXINS PRODUCED BY BACTERIA 



last may explain, in part at least, the anaemias so common in 

 the associated diseases). In the action of many of these toxins 

 the occurrence of a period of incubation between the introduction 

 of the poison into the animal tissues and the appearance of 

 symptoms is often a feature. 



We have seen that in certain cases there is difficulty in under- 

 standing the action of bacteria which do not form toxins in fluid 

 media, especially as in the cases of some of these the bacterial 

 protoplasm does not seem very toxic. Yet we often see effects 

 produced at a distance from the focus of infection, e.g. in 

 anthrax. To explain such occurrences it has long been put 

 forward as a possibility that some bacteria are only capable of 

 producing toxins within the animal tissues, and it has further 

 been thought possible that bacteria, such as, for example, the 

 typhoid bacillus, which do in media give rise to intracellular 

 toxins, might either produce these toxins more readily in the 

 tissues or might produce in addition other toxins of a different 

 nature. Recently such toxins have been much studied, and the 

 name aggressins has been given to them. The evidence adduced 

 for the existence of these aggressins as a separate group of bacterial 

 poisons is of the following kind. An animal is killed by a dose 

 of the typhoid, dysentery, cholera, or tubercle bacillus, or by a 

 staphylococcus, the organism being introduced into one of the 

 serous cavities. After death the serous exudation, which in all 

 these cases is present, is removed, and centrifugalised to remove 

 the bacteria so far as this can be done by such a procedure ; 

 the bacteria which are left are killed by shaking the fluid up with 

 toluol and leaving it to stand for some days. It is stated that 

 such a fluid is of itself without pathogenic effect, but has the 

 property of transforming a non-lethal dose of the bacterium used 

 into one having fatal effect. Further, the effects of the combined 

 actions of the bacteria and aggressins are often of a much more 

 acute character than can be obtained with toxic products 

 developed in vitro. Thus, in the case of the action of a non- 

 lethal dose of the tubercle bacillus plus its aggressin, death may 

 occur in twenty hours, a result never obtained with artificial 

 cultures of the organism. The results obtained are attributed 

 to a paralysing action which the aggressin is supposed to have 

 on the phagocytic functions of the leucocytes. The subject is 

 full of difficulties, and in the case of certain of the organisms 

 employed, it is stated that results similar to those attributed to 

 aggressin action have been observed with macerated cultures, 

 the deduction being that in the aggressins we are merely deal- 

 ing with concentrated intracellular toxins. On the other hand, 



