INTRACELLULAR AND EXTRACELLULAR TOXINS. 173 



been revealed by the study, partly of the bodily tissues of 

 animals infected by the bacteria concerned, partly by what 

 occurs in artificial cultures of these bacteria. The dead bodies 

 of certain species have been found to be very toxic. When, for 

 instance, tubercle bacilli are killed by heat and injected into a 

 susceptible animal tubercular nodules are found to develop round 

 the sites where they have lodged. From this it is inferred that 

 they must have contained characteristic toxins, seeing that 

 characteristic lesions result. The bodies of the cholera vibrio 

 are Ukewise toxic. Such intracellular toxins, as they have been 

 called, may appear in the fluids in which the bacteria are living 

 (i) by excretion in an unaltered or altered condition, (2) by the 

 disintegration of the bodies of the organisms which we know are 

 always dying in any bacterial growth. Sometimes, on the other 

 hand, the media in which bacteria are growing become extremely 

 toxic. This is much greater in some cases than in others. The 

 two best examples of bacteria thus producing soluble toxins are 

 the diphtheria and tetanus bacilli. In these and similar cases, 

 when bouillon cultures are filtered bacterium-free by means of a 

 porcelain filter, highly toxic fluids are obtained, which on injec- 

 tion into animals reproduce the highly characteristic symptoms 

 of the corresponding diseases. In the case of the B. anthracis 

 and of many others, at any rate when growing in artificial media, 

 such toxin production is much less marked, a filtered bouillon 

 culture being relatively non-toxic. It is probable, however, that 

 this may not occur when the bacillus is growing in an animal 

 body, for we have often here well-marked evidence of pathogenic 

 effects being produced at a distance from the actual focus of 

 bacterial growth. This is further an instance of what we have . 

 strong reason to believe sometimes occurs, namely, that the 

 toxins produced by bacteria, when these are growing in the ani- 

 mal body, differ somewhat from the toxins produced by the 

 same bacteria growing in artificial media. Poisons appearing in 

 cultures have been called extracellular toxins, but, as we shall 

 see, we cannot as yet say whether they are excreted by the 

 bacteria, or whether they are produced by the bacteria acting on 

 the constituents of the media. We therefore cannot as yet draw 

 a hard and fast line between intra- and extracellular toxins, but 

 the terms are convenient, and may apply to two actually 

 different sets of bodies. That the poisonous capacities of a 



