THE INFECTIOUS DISEASES. 263 



Other Bacteria of the Diphtheria Bacillus Group. 



While the diphtheria bacillus varies greatly in the physiological capacities which 

 determine its virulence, its general morphological and cultural characteristics are fairly 

 constant. There are, however, non-virulent bacilli occurring on mucous membranes 

 under normal as well as abnormal conditions which considerably resemble this, but 

 which differ somewhat in both morphological and biological characters from the true 

 diphtheria bacillus and its variants. Such organisms have been called pseudo-diphthma, 

 bacilli. These non-virulent forms may be regarded as attenuated varieties of the diph- 

 theria bacillus. 



The so-called Xerosis bacillus, which has been repeatedly found in xerosis conjunc- 

 tivae, is apparently a member of the diphtheria bacillus group. 



TETANUS. (Lockjaw.) 



This disease, which is especially marked clinically by muscular spasni^ 

 is due to infection by the jjacillus tetani. This organism is rather wide- 

 spread and in some places very abundant, occurring with other germs in 

 the soil, especially in manured soil, and gaining entrance to the body 

 through wounds, which are often very slight. The soil in certain regions 

 appears to harbor in especial abundance the tetanus organism or its 

 spores. Thus in certain districts on Long Island and in New Jersey 

 slight injuries are frequently followed by tetanus. The liability to in- 

 fection from the spores is greatly enhanced by their association with 

 other organisms or with dirt, splinters, etc., in the wound. 



THE LESIONS OP THE DISEASE. 



The local lesion in tetanus is usually slight and not characteristic, 

 often consisting only in a slight suppuration. 



The morphology of the lesions of the nervous system to the existence 

 of which the symptoms of tetanus so directly point is yet obscure. Over- 

 filling of the blood-vessels, cellular exudate into the perivascular spaces, 

 chroniatolysis of the ganglion cells of the spinal cord are common. The 

 T5acillus remains for the ^most part at the seat of .local lesion and induces 

 its effects by the elaboration of a most intense poison or toxin, called 

 M no-toxin. The action of this toxic substance appears sometimes to 

 continue in the body after the death of the organisms which have elabor- 

 ated it. This infectious disease affords a most typical example QJL. 

 toxaemia. 



Characters of the Bacillus Tetani. 



It is rather long, slender, and motile, often growing in pairs or threads and prone 

 to develop a spore in one end (Fig. 135), in which condition the bacillus is larger at this 

 end, being club- or racKet-shaped. It is readily stained. At the room temperature it 

 grows on artificial culture media, and is strictly anaerobic, flourishing in an atmosphere 

 of hydrogen. It fluidifies gelatin after sending out into it irregular-shaped, ray-like 

 outgrowths. 



The spores of the tetanus bacillus are very resistant to drying, to heat, and to vari- 

 ous chemical disinfectants. 



