282 OTHER GERM DISEASES. 



results left no loophole for criticism, proving that this bacterium was 

 the cause of anthrax, and thus for the first time demonstrating that 

 an infectious disease was produced by a bacterium multiplying 

 within the body of the animal in which it grows as a parasite. 



The bacterium in question, Bact. anthracis, is a rod of moderate 

 size (Fig. 52). It multiplies by repeated division, the elements re- 

 maining attached to form long chains. Sometimes these long 

 threads show no signs of the divisions, and in certain media they 

 form marvelously twisted and contorted masses. When in an 

 active growing condition, this bacterium is readily killed by ordinary 

 disinfecting agents and by a moderate heat, a temperature of about 

 1 60 F. easily destroying the rods. But it produces resisting spores 

 which can easily be distinguished inside the rods as clear, glistening 

 bodies. It is their resistance to ordinary agents that makes anthrax 

 so persistent, and this high resistance must be borne in mind when 

 the attempt is made to disinfect a stable which has been occupied by 

 an animal having this disease. These spores will resist the action of 

 5 per cent, carbolic acid solution for half an hour, or a i per cent, 

 solution of corrosive sublimate for about the same length of time. 

 Few other living bodies can resist such treatment. The spores will 

 also resist a temperature of about 280 F. for two or three hours. 

 When immersed in liquid they are much more easily killed, since the 

 temperature of boiling, if maintained for a few minutes, is com- 

 monly sufficient to destroy them. When dried the spores may 

 remain alive for a long time, many years at least, and yet all the time 

 retain their power of developing when placed under proper condi- 

 tions. All of these facts evidently make the disinfecting of an 

 infested locality a matter of very great difficulty. 



Method of Infection. Although this disease is extremely fatal, 

 animals affected rarely recovering, it is not particularly contagious, 

 and is rarely commuriicated directly from animal to animal. One 

 common method by which cattle are infected appears to be through 

 the food which they crop in the fields. It has often been noticed 

 that the disease breaks out in a herd shortly after it has been turned 

 out into a new pasture. In some of these cases which have been 

 investigated the explanation is simple. In such pastures bodies of 



