TEXT-BOOK OF BACTERIOLOGY. 315 



pi^s. Local symptoms in all cases are followed by bloody oedema, 

 hemorrhages into the tissue of the lymph glands, and effusions into 

 the pleural cavities. 



The animals are sick only a short time, guinea- pigs perishing 

 after twenty-four to forty-eight hours. The process in rabbits is 

 usually somewhat slower; days and even weeks elapse before 

 death ensues. The general symptoms are thus allowed time and 

 opportunity to develop. Inoculation is succeeded (in rabbits 

 most frequently, but also in Guinea-pigs and pigeons) by paral- 

 yses reminding us of those observed in human diphtheria. Soon 

 after injection into the trachea the animals begin to have a 

 rattling in the throat; the breathing becomes difficult and more 

 rapid; food is refused ajid the temperature rises considerably; 

 when death occurs the walls of the trachea are lined with mem- 

 brane down to the larger bronchi. If the end is delayed, or the 

 animals recover, symptoms of incipient paralysis will be perceived 

 on about the sixth or seventh day. The extremities (first the pos- 

 terior, then the anterior) are dragged along and gradually become 

 paralytic. Disturbances of co-ordination will finally supervene 

 and will quickly lead to the end, even in animals apparently 

 cured. 



The rods are regularly found only in the immediate neighbor- 

 hood of the point of infection, while the blood and internal organs 

 are always entirely free from micro-organisms, as is the case in 

 human diphtheria. 



The results of transmission do not, however, correspond to this 

 description under all circumstances. A difference in the pathogenic 

 effect has been observed under natural conditions (just as with 

 FraenkePs pneumonia bacteria) and it has been ascertained, more- 

 over, that the diphtheria bacilli very rapidly succumb to nat- 

 ural attenuation. Its adaptation to an artificial culture-medium 

 (mentioned before) goes hand in hand with a loss of virulence. The 

 more the bacteria extend on the agar-surface, the more their 

 strength will diminish; although exceptions to this rule are occa- 

 sionally met with and a still undiminished virulence may be per- 

 ceived in old cultures. 



The purely local occurrence of diphtheria bacilli and the severe 

 general symptoms caused by them (as pointed out above) can only 

 be explained by the supposition that the bacteria generate a solu- 

 ble substance which spreads from their locality through the body 

 and thus affects even remote parts. This view has, in fact, been 

 proved correct by recent investigations. 



Roux and Yersin found that the germ-free filtrate of somewhat 



