PART I. 



THE PROG11ESS OF KNOWLEDGE WITH REGARD TO THE 

 FERMENTS AND MICRO-PARASITES DURING RECENT YEARS. 



THE first undoubted observation as to the existence of The earliest 



-,.... . _. observations 



small microscopical living beings in our surroundings was with regard 

 made by Ehrenberg, who found numerous organisms 

 in water and in dust, and designated them " Infusion 

 animals (Infusionsthierchen, 1828)." Eight years later 

 the vegetable nature of yeast was discovered by Caignard- 

 Latour and Sclnvann, although the cell form had been 

 seen much earlier (first by Leeuwenhoek, 1680), and 

 their organised and vegetable character had been sus- 

 pected by several investigators (Thenard, Persoon). 

 Schwann also, in the year 1837, asserted as the result 

 of experiments, that the atmospheric air was constantly 

 laden with fermentative and putrefactive germs, and also 

 that certain fermentative processes were dependent on 

 the access of living organisms. 



From that time dates the lasting and active interest 

 in micro-organisms, and the development of the subject 

 has chiefly taken two different directions : on the one 

 hand, the problem investigated was the relation between 

 the fermentative germs and the processes of fermentation 

 and putrefaction ; on the other hand, the attempt was 

 made to demonstrate a causal connection between similar 

 minute living bodies and infective diseases in man and 

 animals, a connection which various hypotheses and 

 analogies rendered probable. It is only possible to 

 follow the numerous controversies with regard to the 

 significance of the micro-organisms by tracing separately 

 the gradual development of knowledge, on the one hand 

 with regard to fermentation, and on the other with regard 

 to parasitic growth. 



