190 TEXT-BOOK OF BACTERIOLOGY. 



we make a cover-glass preparation of sucli a colony, we see that 

 all these branches and outgrowings of the little culture come out 

 as colored markings. A stronger magnification with oil immersion 

 will show that the ramifications consist of separate rod-cells ar- 

 ranged in strings, which in their rapid growth yield such strange 

 forms and figures. 



It is true that it is not easy to get preparations in which all this 

 is clearly displayed. The liquefaction of the gelatin is exceedingly 

 rapid and spreads widelj^ ; it requires four or five dilutions to yield 

 a plate not too crowded, and even then it is often difficult to select 

 the right moment for observation. 



In the test-tube culture the liquefaction of the gelatin proceeds 

 evenly from the puncture and soon the entire contents of the tube 

 are melted. At the surface a thick" layer of whitish-gray, cloudy 

 substance collects, but does not advance to the formation of a crust. 

 Under it is a somewhat clearer fiuid, and at the bottom lies the 

 chief mass of the culture in flakes and crumpled portions. Agar 

 is quickly covered over with a moist, shining, grayish-white thin 

 coating. On potatoes a dirty- colored, fatty coating appears, which 

 has no peculiarities worthy of note. 



This bacillus thrives excellently in the incubator; on media rich in 

 albumin it forms poisonous excretions, and hence has toxic qualities. 

 If we introduce a considerable quantity (3 to 5 cm.) of such cultures 

 into the peritoneal cavity of a rabbit or Guinea-pig, or if we inject 

 it into the blood of these animals, they perish in a short time. A 

 dissection often shows symptoms of acute peritonitis or of a well- 

 pronounced inflammation of the intestinal mucous membrane. 



The Proteus vulgaris is the species against which Foa and 

 Bonome were able to grant immunity by means of a definite chem- 

 ical substance. An increased power of resistance on the part of an 

 animal against a strictly toxic micro-organism such as the proteus, 

 can only be brought about by gradually accustoming the animal to 

 the poison. Foa and Bonome proceeded from the a priori suppo- 

 sition that neurin was a chief product of the proteus. Their exper- 

 iment succeeded; they were enabled, by the use of this substance, 

 to bring about immunity against the effects of proteus cultures. 



The proteus species (vulgaris, mirabilis, and Zenkeri) discovered 

 by Hauser have since been increased by others (Proteus hominis and 

 P. capsulatus) which have been particularly studied by the Italian 

 investigators Bordini-Uffredu/.zi and Banti, and which play a part 

 in human diseases. It would lead us too far to enter into a partic- 

 ular description of them here. Suffice it to saj- that they seem to be 

 inhabitants of the intestinal canal which are harmless under ordi- 



