506 EEPORT OF THE COMMISSIONER OF AGRICULTURE. 



tube. It is densest in nentralized meat infusion to which 1 per cent, of 

 peptone has been added, and appears in the form of whitish downy 

 masses which are readily shaken down into the liquid. On the surftice 

 no confluent membrane forms, but occasionally a small i)atclj, resem- 

 bling the band just described, is seen floating" on the surface of the liquid. 

 This band cannot be horaologized with the membrane formed by other 

 bacteria, such as that of haciUus subtilis, since it is not constantly present 

 and forms only after several days or a week. It must be looked upon 

 merely as a deposit of the bacteria similar to that formed on the bottom 

 of the tube at the same time.* At the end of two or three weeks the 

 sediment, consisting entirely of very short rods or ovals, does not stain 

 well. Only a narrow line of color indicates the outlines of the individ- 

 ual microbes. It might be claimed with Klein that these are spore- 

 bearing forms. This, however, has not been confirmed. On the other 

 hand, our experiments on the thermal death point, given below, oppose 

 this view. 



When soM^ on gelatine plates, either scattered or in lines, the colo- 

 nies may be detected with a low power after forty-eight hours. They 

 are nearly spherical, with pale disk and sharply-detined margin. In an- 

 other day they are visible to the naked eye as mere points. Examined 

 with a 1-inch objective they appear irregularly oval, egg-shaped, or 

 spherical. The margin is a well-defined dark line, the disk brownish in 

 color with transmitted light (Plate II, Fig. 2 a). When growing on the 

 surface, the colonies appear as patches somewhat refrangent (Plate II, 

 Fig. 2 h). The center being elevated, the whole forms a very fiat, irreg- 

 ular cone. The border of the colony is irregular, very thin, and pale. 

 While examining liquid cultures by sowing them in lines on gelatine 

 plates, W8 observed in every line a few very faint, cloudlike bodies, 

 which were evidently situated near the lower surface of the gelatine, or 

 between it and the glass. These colonies (Plate II, Fig. 2, c, c', c") were 

 much larger than the s])herical forms, the center slightly opaque and 

 margins gradually vanishing. We at first suspected the presence of 

 another microbe, but how could two microbes be present in a liquid cult- 

 ure in the proportion of 1 to 100 or more? When examined microscop- 

 ically they resembled the bacterium which was in the majority. Yet 

 this method was not satisfactory, since it was difficult to get access to 

 the deeply buried colony. Finally, we came to the conclusion that the 

 bacterium of swine plague grew in this way when deposited on the glass. 

 To lU'ove this, we dried thin layers from a liquid culture upon glass 

 plates and poured the gelatine upon them. In forty-eight hours we 

 found the plates covered with these pale, nebulous colonies; only a very 

 small number were round. As the film had not been thoroughly dry, 

 some bacteria may have worked their way into the gelatine and there 

 developed into spherical colonies.- 



There is another feature of the nebulous colonies which suggested to 

 us the identity of the two forms of growth. In Figure 2 c" a nebulous 

 colony is drawn with> a spherical form above but communicating with 

 it. At first sight the spherical form seems to have burst and discharged 

 its contents, which represent the nebulous form, the true explanation 

 being that the same colony grows up into the gelatine and laterally over 

 the glass. Figure 2 c', represents another form of colony very frequently 

 observed, in which the connection between the two parts does not ap- 

 pear, but undoubtedly exists below. Owing to a lack of time, it has not 



* We have lately observed ia a few tubes -wliich stood undietiirbod over a \f©ek, a 

 Oiore or less complete surface membrane, composed of very brittle fragments. 



