THE MICKOBES OP HUMAN DISEASES. 217 



sources. The former multiplied rapidly and energeti- 

 cally, succeeding each other up to the tenth generation, 

 while those from Philadelphia only went to the fourth 

 or fifth generation, and those taken from the tongue 

 did not go beyond the third. It must be observed that 

 the diphtheritic angina of Philadelphia is much less 

 fatal than croup, and the first attempts at inoculation 

 made by Formad and Wood produced doubtful results, 

 precisely because they were made with the microbe 

 of diphtheritic angina, which is an attenuated form 

 of the microbe of croup. The organism is the same, 

 but it is modified by the medium in which it is 

 developed, and the vitality of artificial cultures is in 

 direct proportion to the malignity of the disease from 

 which the germs for sowings are derived. 



The following theory may be deduced from these 

 facts, which will explain all cases of diphtheria : — A 

 child contracts a simple catarrhal angina, or laryngitis; 

 the micrococci, which up to this time remained inert 

 in the mouth, begin to grow and multiply under the 

 influence of the inflammatory products which favour 

 their development ; the plant which has been dormant 

 becomes widely diflfused. There are many degrees 

 between croup with malignant complications and the 

 mildest form of diphtheritic angina, as all practical 

 physicians know. More or less numerous germs of 

 micrococci float in the air, or — which appeared to be 

 the case at Ludington — are conveyed in drinking- 

 water, and they may encounter more or less favourable 



