Q]ST SOME NEW MICRO-ORGANISMS OBTAINED FROM AIR. 
259 
first step in investigations of this kind must consist in such careful delineation of the 
characteristics of specific organisms that their identification may be readily 
accomplished. In this way it may with confidence be anticipated that the particular 
chemical and physiological properties of each specific organism will in the future be 
elaborated, as has been done in a few cases already. It has been especially with this 
object in view that we have undertaken the task of collecting from the air a number 
of different varieties of micro-organisms, and, after isolating and obtaining them in a 
pure state, to carefully delineate the characteristic appearances which they present, 
both under the microscope and when grown in various cultivating media. 
Methods of Study and Examination. 
The organisms which we have made the subject of special study were obtained 
in the examination of the air of various places by means of Hesse’s tubes, and by the 
exposure of dishes filled with gelatine-peptone in the manner already described. In 
both cases the aerial organisms are deposited on the surface of the solid gelatine, 
and, by incubation for several days, each organism thus deposited gives rise to a 
colony frequently possessing a characteristic appearance. If these colonies are not 
too closely crowded together on the surface of the gelatine, it is easy to transfer a 
small portion of a single colony to a culture-tube without any admixture from adjacent 
colonies. This transference is most conveniently effected by means of a sterilised 
platinum-needle. As the colonies obtained in the Hesse’s tubes or on the gelatine 
dishes are, as already pointed out by one of us, invariably pure, the cultivation which 
is obtained by inoculating the needle into a sterile culture-tube is also pure if the 
operation of transference is performed with care and in an atmosphere reasonably 
free from dust. Thus in the hundreds of cultivations which this investigation has 
ehtailed we have scarcely had a single instance of a culture being vitiated through 
contamination from the air during the process of transference and inoculation. 
Gelatine tube-cultivations .—The colonies originally obtained from the air were 
invariably inoculated, in the first instance, into test tubes, one-third filled with solid 
sterile gelatine-peptone (for preparation of which see below), and plugged with cotton 
wool in the ordinary way. The appearances in these gelatine tubes have been carefully 
watched, described, and in many cases drawn. These appearances are, as is well 
known, of great hnportance in serving to characterise specific organisms, and 
frequently serve to discriminate between organisms cf similar and almost identical 
microscopic appearance. 
Composition of Cultivating Media employed :— 
Gelatine .—100 grms. gelatine; 10 grms. peptone (dry) ; common salt, 1 grm.; lean beef, 1 lb.; water 
1 litre. 
Agar-agar .—10 grms. agar-agar instead of the gelatine; otherwise identical. 
Broth .—Similar to the above, only omitting the gelatine or agar-agar. 
2 L 2 
