DEVELOPMENT OF THE GERM THEORY. 23 



Among chemical actions, it is chiefly the processes of fermen- 

 tation and decomposition which, by their capacity for extension by 

 means of the smallest possible quantity of matter, show the most 

 striking analogy to contagious diseases ; and we know now that 

 these ferment processes are all associated with the multiplication 

 of low organisms, so that the theory of fermentation becomes vir- 

 tually identical with the theory of a contagium vivum, 



Liebermeister insists on the fact that contagious diseases never 

 originate spontaneously, but are dependent on a transmission, a 

 continued propagation, of a disease-poison. He notes also that 

 the contagious diseases of the silkworm have been proved to be 

 parasitic, and the history of the development of the parasite has 

 been followed pretty thoroughly; but he omits altogether any 

 reference to Pasteur, whose work this was, and in his search for 

 proofs for his theory is apparently ignorant of the work of Lister 

 in this country. 



Immense advances have been made since 1875 ^^ ^^^ discovery 

 of the special micro-organisms of the diseases then recognised as 

 infectious, and many additions have been made to the list of these 

 latter. The denizens of this invisible world which have so long 

 escaped observation are now being dragged into the light of day 

 and subjected to the closest investigation. The study of micro- 

 organisms has become a necessary part of medical education, and 

 attempts at classification have been made, and many terrible and 

 prodigiously long names coined to express withal the groupings, 

 functions, and forms of these little beings. 



To enable students to pursue these studies with greater ease, 

 the German Government spent ^12,000 in bringing the lens to a 

 higher state of perfection, with the result of obtaining one abso- 

 lutely achromatic. 



For the first year they kept the secret of this wonderful lens, 

 and then gave it to the world. With such a lens and by staining 

 the objects under the cover-glass, it is easy now to detect the 

 presence and study the ways and habits of these micro-organisms.* 

 It is undoubtedly to Pasteur that the credit is due for the early 

 discoveries in bacteriology. He proved that not only did water 

 teem with life — this had long been known — but that the air around 



* Tke Reahn of the Microbe (Priestley). 



