MODE OF SPREAD OF INFECTIVE DISEASES. 733 



with anthrax it is evident that healthy animals do not easily 

 become affected, even when they live in close contact with 

 the diseased ones. On the other hand, in intestinal anthrax 

 quantities of dejecta containing anthrax spores are poured 

 out on the meadows from which healthy animals obtain their 

 food, and thus it is easy to understand how the disease 

 spreads by the spores which are preserved in the grass. In 

 like manner in burying the bodies of animals which have 

 died of anthrax, and which have been opened, blood, &c., may 

 be left on the surface of the soil, and spores subsequently 

 form there and ultimately get into the fodder. While, how- 

 ever, in this mode of spread the pathogenic agents are as a 

 rule ultimately killed or interfered with by some meteoro- 

 logical influence, it is probable that there are some natural 

 abodes of the anthrax bacilli where they multiply outside the 

 body and constantly form new spores, these abodes being 

 therefore dangerous and permanent reservoirs ; situations 

 of this kind are present in the neighbourhood of rivers and 

 marshes, where sufficient moisture, favourable temperature, 

 and a plentiful supply of dead vegetable substances are 

 present, and thus in exceptional cases a saprophytic growth 

 of anthrax bacilli can take place. From these situations the 

 spores may be transported to meadows by means of floods, 

 and there give rise for a series of years to outbreaks of 

 disease, although the multiplication of the infective agents 

 may be limited to the body of the diseased animal. In the 

 case of man, as is well known, infection with anthrax occurs 

 almost exclusively by means of the bacilli and spores developed 

 in the diseased animal, and adhering to the skin, hairs, &c., 

 and the fact that the formation of the spores occur for the 

 most part after the death of the animal does not in any way 

 detract from the contagious character of this mode of spread. 



Various other infective agents may show a certain Parasites 

 amount of saprophytic growth, which, however, is of less Jj}]" 5 ^ J^JJJ 

 importance as regards their spread than in the case of saprophytic 

 typhoid fever, cholera, and anthrax. The staphylococci gl 

 are very widely distributed ; but it is relatively unimpor- 

 tant whether their number increases only as the result of 

 constant reproduction in pus, or also as the result of 

 saprophytic growth. The streptococci, erysipelas cocci, 

 &c., are able to multiply on dead nutrient substrata 

 under favourable conditions ; but the usual mode of 

 spread to healthy individuals is nevertheless either in 

 the fresh state by contact, instruments, &c., or in the 



