PATHOGENIC EFFECTS 377 



Pathogenic Effects. The proof that the b. tetani is the cause 

 of tetanus is complete. It can be isolated in pure culture, and 

 when re-injected in pure culture it reproduces the disease. It 

 may be impossible to isolate it from some cases of the disease, 

 but the cause of this very probably is the small numbers in 

 which it sometimes occurs. 



(a) The Disease as arising Naturally. The disease occurs 

 naturally, chiefly in horses and in man. Other animals may, 

 however, be affected. There is usually some wound, often of a 

 ragged character, which has either been made by an object 

 soiled with earth or dung, or which has become contaminated 

 with these substances. There is often purulent or foetid dis- 

 charge, though this may be absent. Microscopic examination 

 of sections may show at the edges of the wound necrosed tissue 

 in which the tetanus bacilli may -be very numerous. If a 

 scraping from the wound be examined microscopically, bacilli 

 resembling the tetanus bacillus may be recognised. If these 

 have spored, there can be practically no doubt as to their 

 identity, as the drumstick appearance which the terminal spore 

 gives to the bacillus is not common among other bacilli. Care 

 must be taken, however, to distinguish it from other thicker 

 bacilli with oval spores placed at a short distance from their ex- 

 tremities, such forms being common in earth, etc., and also met 

 with in contaminated wounds (Fig. 124). It is important to note 

 that the wound through which infection has taken place may be 

 very small, in fact, may consist of a mere abrasion. In some 

 cases, especially in the tropics, it may be merely the bite of an 

 insect. The absence of a definite channel of infection has given 

 . rise to the term " idiopathic " tetanus. There is, however, 

 practically no doubt that all such cases are true cases of tetanus, 

 and that in all of them the cause is the b. tetani. The latter 

 has also been found in the bronchial mucous membrane in some 

 cases of the so-called rheumatic tetanus, the cause of which is 

 usually said to be cold. 



The pathological changes found post mortem are not striking. 

 There may be haemorrhages in the muscles which have been the 

 subject of the spasms. These are probably due to mechanical 

 causes. Naturally it is in the nervous system that we look for 

 the most important lesions. Here there is ordinarily a general 

 redness of the grey matter, and the most striking feature is the 

 occurrence of irregular patches of slight congestion which are not 

 limited particularly to grey or white matter, or to any tract of 

 the latter. These patches are usually best marked in the grey 

 -matter of the medulla and pons. Microscopically there is little 



