228 PASTEUR: THE HISTORY OF A MIND 



to the scientific man whom one most willingly cites as 

 the immediate precursor of Pasteur, to Henle who, 

 about 1840, published a sort of theory of disease, the 

 developments of which seem in fact in harmony with 

 our present ideas. For Henle, the evolution of a disease 

 is in all respects comparable to that of a living being. 

 The quantity of morbid matter which may produce it in 

 a healthy individual, like the seed of the plant or animal, 

 is out of all weighable proportion to the quantity of effect 

 produced, and to the quantity of morbid matter which 

 the diseased individual produces in his turn. An acorn 

 produces an oak, which yields in its turn a multitude 

 of acorns. 



So much for a first point of view. Here is a second: 

 Between the time when the morbid matter enters into 

 the body, and that in which it is translated into dis- 

 orders preceding disease, a period intervenes which is 

 well known under the name of period of incubation, which 

 is nearly constant for each disease, and differs from one 

 disease to another. How is it possible not to connect 

 it with the duration necessary for the development of 

 the germ and the infection of the tissues? How explain 

 it otherwise than by the doctrine of parasitism? So 

 long as the disease lasts, he who has it must be a source 

 of contagium. When it has ceased, all danger of conta- 

 gion ceases. This means that the germ is dead and can 

 no longer injure. The same for epidemics. In their 

 appearance, their extension over a territory more or less 

 great, their lingering termination, do they not resemble 

 absolutely the beginning, the middle and the end of a veg- 

 etation, and is it not remarkable also that many disin- 

 fectants and even remedies should be at the same time 

 active agents of destruction of vegetable or animal life? 



Behold, it has been said, an unlettered print of the 

 system of Pasteur, and that which makes still further 





