1893.] Bacteriology in its General Relations. 1051 
found its greatest development in the employment by Koch, 
of gelatin as a transparent solid medium for the isolation and 
cultivation of germs. Some features of this method had been 
anticipated by other workers, especially Klebs. 
This method enables the experimenter to isolate the form 
he desires to study from any mixture of different species, and 
by cultivating it in sterile media, a pure culture derived from 
a single germ can be obtained which is made the basis of defi- 
nite morphological and physiological study. Brefeld’s meth- 
ods of studying the morphology and developmental history of 
the fungi are essentially the same as the bacteriological cul- 
ture methods. He first obtained his pure cultures by dilution 
until he had à single germ. Later he added the use of gela- 
tine or other transparent ingredients as a means of isolating 
and fixing the developing organism. The results of these 
studies which now fill ten large quarto volumes, are among > 
the greatest contributions to mycology, that this century has 
produced. He refused to admit the validity of the classic 
descriptions that had been based upon material gathered 
under natural conditions, maintaining that the systematic 
part of the science was full of errors, that had arisen from the 
examination of imperfect mixed growths, and the separation 
of different growth-forms into individual species. 
Basing his opinion upon the only scientific foundation, 
that we must know the complete life history of a form 
before we can intelligently study its phylogenetic affinities, he 
made his observations upon pure cultures grown from a sin- 
gle spore in sterile nutrient media. These he kept from the 
‘original spore until in many cases.the fruiting process had 
been completed. By this method he was able to settle defi- 
nitely many disputed points concerning the value of certain 
form-genera and species. "These conclusions of Brefeld, based 
upon the single cell, pure culture method, have revolutionized 
the entire classification of the great group of fungi and the 
theories as to the phylogenetic affinities of different groups have 
been greatly modified. Hansen adopted the same method in 
his study of ferment organisms, more especially the yeasts, and 
this plan of pure culture growths has settled many controver- 
