78 Infection 



of the operation of other micro-organisms, and a recognized type 

 of disease results, it becomes possible to say that the micro-organism 

 in question is specific. 



The most striking examples of the specific action of bacterio- 

 toxins is, however, seen in those cases where soluble extracellular 

 metabolic products of bacterial energy are liberated into the body 

 juices so as to be conveyed by the circulatory system to all parts 

 of the body. Those cells most susceptible to its action are then 

 first or most profoundly impressed by it, and definite responses 

 brought about. Thus, the soluble toxin of tetanus causes no visible 

 reaction in the cells with which it first comes into contact at the 

 seat of primary infection, because these cells are either less sus- 

 ceptible to its influence, or are less well able to show its effects, 

 than the cells of the nervous system to which it is secondarily carried 

 by the blood. 



SPECIFIC AFFINITY OF THE CELLS FOR THE TOXINS 



The cells of the connective tissue in which the tetanus bacillus 

 is Uving show little reaction, but the motor cells of the central 

 nervous system, having a greater affinity for it, are profoundly 

 impressed, so that convulsions of the controlled muscular system 

 are brought about. This special excitation of the nerve cells is 

 specific because no other bacterio-toxin is known to produce it and 

 it is attributed to special selective affinities of the nerve cells for 

 the poison. This affinity has its analogue among the poisons of 

 higher plants, thus, strychnin has a similar selective affinity and is 

 also said to be specific in action upon the motor cells. 



The venoms of various serpents, especially the cobra, also have 

 specific reactions, the cells of the respiratory centers seeming to 

 be most profoundly affected by them. 



The diphtheria bacillus, when observed in ordinary throat in- 

 fections, is seen to produce a pseudomembranous angina which 

 results in part from an irritative local action of the organism, which 

 it shares in common with many others, and in part from some 

 coagulating product which it shares in common with a few — 

 pneumococcus, streptococcus, etc. Neither of these reactions is 

 specific, but subsequent to these early manifestations comes de- 

 pressant action on the nervous cells with palsy, peculiar to the prod- 

 ucts of the diphtheria bacillus, and therefore specific. 



It is upon the peculiar specific reactions of the bacterio-toxins 

 and the peculiar susceptibility of certain cells to this action that the 

 production of distinct clinical manifestations depend. 



THE INVASION OF THE BODY BY MICRO-ORGANISMS 



Some bacteria whose invasiveness is insufficient to enable them 

 successfully to maintain life in healthy tissues, occasionally get a 



