672 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



former. It will also be remembered that after one or two weeks a 

 ring of deposit forms about the tube at the surface of the liquid in 

 the culture of the hog-cholera bacterium. In a few cultures an 

 incomplete surface membrane may also appear. It multiplies more 

 abundantly, therefore, in this medium than the more delicate microbe 

 under consideration. 



If a drop from a culture one day old be examined with a ra 

 homogeneous objective no spontaneous movemenl^ can be observed. 

 When dried and stained in an aqueous solution of methyl violet or 

 other aniline, the microbes are best studied, as regards their form, at 

 the circumference of the dried film, where they have been drawn 

 together in large numbers by the slov/ drying of the drop. The 

 microbe appears in the form of an oval coccus, about .6 to .7 micro-, 

 millimeter long and .4 micromillimeter broad. The small size 

 makes the exact measurement very difficult. Besides these there are 

 smaller and larger forms measuring 1 micromillimeter in length. 

 The great majority of forms correspond with the dimensions first 

 given. Those around the border of the dried film usually show the 

 characteristic stain at the extremities with the unstained band be- 

 tween. The remainder are usually so small that this cannot be made 

 out, or else they are in that stage of growth when division has not 

 yet begun, and are uniformly colored. 



If a minute portion from the organs of a rabbit, or from a culture 

 of this microbe, be shaken up with nutrient gelatine, barely lique- 

 fied by a gentle heat, and the mixture poured on plates, the colonies 

 will become visible to the unaided eye in about two days, provided 

 the temperature does not fall below 70° F. They are round, with 

 pale homogeneous disk, when examined with transmitted light. Their 

 growth is slow, and at the end of a week they vary in diameter from 

 ^""° to i™"\ Their appearance at this age is peculiar (Plate IV, Fig. 5). 

 Each colony is provided with a border of varying width, usually not 

 exceeding one-fourth the radius of the colony. This border is paler 

 than the central portion, and sharply separated from it by a circular 

 line, sometimes slightly eccentric, as in the illustration. The central 

 disk is usually somewhat granular at this stage. The colonies when 

 growing on the surface of the layer of gelatine spread quite rapidly, 

 and soon are four or five times the size of the deep colonies. The 

 margin of the more or less circular patch is very thin and sharp, and 

 slightly wavy. This microbe does not liquefy the gelatine at any 

 time of its growth. 



In tubes containing nutrient gelatine the microbes carried by the 

 needle into the depths of the gelatine develop into spherical colonies 

 which do not become larger than i-'""' in diameter (Plate IV, Figs. 1, 

 2). The surface growth is quite vigorous. It spreads as a pearly 

 white circular pa,tch in all directions from the point of inoculation. 

 This patch is not convex, but uniformly thick, usually with a wavy 

 or scalloped border (Plate V, Fig. 1, b). The growth is very slow as 

 a rale, varying with tlie temperature of the room. It requires sev- 

 eral weeks for a disk a few millimeters in diameter to form, and from 

 one to two months for one 5™"' to 10"'"'. When viewed obliquely very 

 faint concentric markings may usually be observed on this pearly 

 growth. There are some slight differences between the tube cultures 

 of the microbe of genuine hog-cholera and this organism, which are 

 entirely exjoressed in the surface growth (Plate V, fig. i^ a, b). In 

 the second annual ro})ort the tube culture of the bacterium of hog- 

 cholera w:as figured as having very minute deep colonies and scarcely 



