THE DOCTRINE OF CONTAGIUM VIVUM. 327 



saprophyte and the other a deadly contagium. We have 

 likewise seen that the spirilla of splenic fever are morpho- 

 logically similar with the Spirochaete plicatilis. We have 

 further seen that there is ground for the assumption that the 

 infective agent in contagious septicaemia is the common bac- 

 terium of putrefaction^ but modified in such a way as to 

 have become endowed with a heightened capacity for grow- 

 ing in the healthy tissues. Do not these remarkable coin- 

 cidences point to a natural explanation of the origin of 

 contagia ? If contagia are organisms, they must necessarily 

 possess the fundamental tendencies and attributes of all 

 organised beings. Among the most important of these at- 

 tributes is the capacity for "variation'^ or ''sporting." 

 Darwin brings forward strong grounds for the belief that 

 variation in plants and animals is not the result of chance 

 or caprice, but is the definite effect of definite (though often 

 quite obscure) causes. I see no more difficulty in believing 

 that the B. anthracis is a sport from the B. subtilis than in 

 believing, as all botanists tell us, that the bitter almond is 

 a sport from the sweet almond ; the one a bland innocuous 

 fruit, and the other containing the elements of a deadly 

 poison. 



The laws of variation seem to apply in a curiously exact 

 manner to many of the phenomena of contagious diseases. 

 One of these laws is the tendency of a variation, once pro- 

 duced, to become permanent, and to be transmitted ever 

 after with perfect exactness from parent to off'spring ; another 

 and controlling law is the tendency of a variation, after 

 persisting a certain time, to revert once more (under altered 

 conditions) to the original type. The sporting of the nee* 

 tarine from the peach is known to many horticulturists. 

 A peach-tree, after producing thousands and thousands of 

 peach-buds, will, as a rare event and at rare intervals, pro- 

 duce a bud and branch which ever after bear only nec- 

 tarines ; and, conversely, a nectarine at long intervals, and 

 as a rare event, will produce a branch which bears only 

 peaches ever after. Does not this remind us of the occasional 

 apparent sporting of diphtheria from scarlet fever ? My 

 friend Dr. Ransonie, who has paid so much attention to the 

 laws governing the spread of epidemics, relates the following 

 instance : — A general outbreak of scarlet fever occurred at a 

 large public school. One of the masters who took the in- 

 fection exhibited diphtheritic patches on the throat. This 

 patient was sent to his own home in Bowden. Six days 

 after his arrival, his mother was attacked, not with scarlet 

 fever, but with diphtheria ; though there were no case§ 



