286 MICROBES, FERMENTS, AND MOULDS. 
only an hypothesis, let us compare it with other hypo- 
theses which have been proposed to explain the 
virulent and contagious nature of certain diseases. 
This comparison may throw some light on the question 
at issue. 
The value of an hypothesis must be estimated by 
the number and importance of the facts of which it 
affords a clear, precise, and really scientific explanation ; 
it must also be estimated by its influence on the 
advance of science. We will therefore enumerate the 
principal theories which have been proposed to explain 
the origin of virulent and contagious diseases, without 
the intervention of microbes. 
Robin's Theory of Blastema.—Although, as far as 
we are aware, Robin has not recently published any- 
thing with reference to his opinion of the value of the 
microbian theory, some of his pupils have set forth the 
theory of blastenia as it was‘ stated by their master in 
books published from ten to twenty years ago. 
In Robin’s opinion, no cell is born from another 
cell, in the form of a bud, an egg, or a spore. Un- 
doubtedly there is no spontaneous generation, at the 
expense of elements of exclusively inorganic origin ; 
but this generation or genesis occurs every day at the 
expense of an organized substance which is living, 
but fluid and amorphous, and which has its source 
from other pre-existent cells. This fluid is termed 
blastema by Robin. Blastema is the surplus of the 
nutritive substance, organized by the cells and exuded 
