852 The American Naturalist. [Ostaber, 
mental disease in infected controls. Subsequently he accom- 
plished the same result in animals of the size of sheep, render- 
ing them resistent to the infection, so that the serum in ade- 
quate quantities can be secured for use in the treatment of the 
human disease. | 
Medical science awaits with intense interest the next step, 
and it is possible that in the near future *the red demon of 
the nursery " will be brought under control. 
Turning from the beneficent results which have been 
secured to medicine, to other lines of activity, the results of 
bacteriological research are equally efficient. Chief among 
these are some results obtained in reference to agriculture. In 
its relation to medicine, bacteriology deals mainly with those 
forms that have adapted themselves to a wholly, or semi-para- 
sitie mode of existence. These however represent but a 
minor fraction of the whole number of species that have been 
isolated. In agriculture, saprophytic, as well as parasitic spe- 
cies enter into consideration, and here parasitism is not con- 
fined to the animal body as a host, but is to be observed in 
plant tissue as well. To the agriculturist then, bacteria come 
in a dual guise. They are both a friend and a foe. Some 
species are to him a direct benefactor, some render him aid in 
a more indirect manner, while others are a positive detriment 
to the success of his calling. How to increase the activity of 
the friendly forms, and diminish the ravages of the noxious 
ones, is the constant study of the agricultural bacteriologist. 
The field, which for convenience we here classify as agricul- 
tural bacteriology, is made up of so many widely separated ` 
subjects, that the detailed methods in one class, cannot be 
successfully utilized in the examination of another. For 
example, the attempt to isolate the organism of nitrification 
which baffled investigators for so long a time, was fruitless 
mainly because they relied almost entirely upon the gelatine 
method of Koch. Each special subject must be studied by 
itself and the technique developed for the method of work in 
establishing the etiology of a bacterial plant, disease differs 
widely from that which must be used in studying the processes 
of nitrification or the fixation of the free nitrogen of the 
