BUREAU OF ANIMAL INDUSTEY. 507 



been possible for us to see whether other microbes, Avhich do not liquefy 

 gelatine, grow in this way on plates. Whether they do or do nor, the 

 matter i.* quite important, and it seems that in future the morphology 

 of colonies, uot ouly within the layer of gelatine and on its surface, but 

 also nnder it, must be studied, if this method is to be continued as ;> 

 means of testing the purity of cultures and determining species. 



In tubes coutainiug nutritive gelatine, these bacteria appear in the 

 form of very minute colonies within two or three days, which enlarge 

 but slightly beyond mere specks (Plate II, Fig. 3). A very thin, whitish 

 glistening layer is usually present on the surface of the gelatine at the 

 point of inoculation, limited to about a millimeter in its surface exten- 

 sion. These minute colonies invariably appear in those cases in whicli 

 the presence of the swine-plague bacterium was determined from cover- 

 glass preparations, and their appearance was alike in all respects. When 

 the culture contained also other bacteria, these usually multiplied more 

 rapidly in the needle track, and the colonies resulting therefrom stood 

 out as large as pins' heads among mere points. The surface growth was 

 then, as a rule, more vigorous and thick: whitish layers were formed. 



When much crowded, the colonies of the swine plague bacterium re- 

 main quite small, while those that are scattered grow considerably larger, 

 They do not exceed half the size of a pin's head even under the most 

 favorable circumstances. "This is readily seen in each tube culture, in 

 which the lowest point of the needle track contains only isolated colonies, 

 while near the surface they are fused into a single mass. This fact must 

 also be borne in mind in estimating the purity of the cultures, as it is ob- 

 viously impossible to subject every section of the needle track to micro- 

 scopic examination. We have found the colonies from the blood almost 

 invariably larger than those from the spleen, chieily because they were 

 always few in number, and also because a small quantity of blood was 

 introduced upon which the bacteria seem to thrive much better than 

 ujion the nutritive gelatine. 



A few additional facts may be mentioned which need further inves- 

 tigation, however. In milk, sterilized by discontinuous boiling, the 

 bacterium multiplies without producing any change in the appearance 

 of the milk itself Two cultures kept for three weeks remained un- 

 changed ; when sown on plates the well-known colonies gTew as usual 

 and were as. abundant as in beef infusion peptone. In two tubes, con- 

 taining respectively 3 and 1.8 per cent, of non-neutralized Liebig's meat 

 extract, the bacterium multiplied rapidly and abundantly. This extract 

 has an acid reaction. The bacterium of swine i)lague, therefore, unlike 

 that of rouget, is not limited to slightly alkaline media, but may grow in 

 those that contain a small portion of acid as well. 



On boiled potato the bacterium grows very well. It seems to be a far . 

 better substratum than beef infusion peptone gelatine. The bacterium 

 manifests growth by first staining the white cut surface of the potato 

 at the place of inoculation with a chocolate color, gradually turning 

 quite dark and spreading over the entire surface. In the latter stage 

 it resembles the discoloration frequentl^^ observed on boiled potatoes 

 standing for a day or two. The growth itself begins in the form of small 

 round masses which gradually unite into a patch ^'""^ to I'"'" thick. This 

 patch spreads slowly by lateral extension and its straw-colored, slightly 

 greenish surface contrasts strongly with the dark, bluish-red background 

 of the potato. This description applies to growth at a temperature of 

 65° to 80° r. In the incubator, at 95° F., the multiplication was more 

 rapid and abundant. 



It grows well in liquid and solid blood serum sterilized by discontin- 



