172 IDENTIFICATION OF BACTERIA 



This is kept in the incubator for twenty-four hours, then well shaken, 

 and a definite fraction of the whole amount used for each animal. 

 (2) An agar tube with a slanting surface is inoculated by rubbing the 

 material thoroughly over the entire surface w r ith the platinum loop. 

 After incubating for twenty-four hours the whole growth is removed 

 with the platinum loop and intimately and uniformly mixed with lO^.c. 

 of an 0.85 per cent, salt solution, a fraction of which is finally inocu- 

 lated into the experimental animals. (3) A platinum loop of definitely 

 known size is used for removing a portion of the growth from an 

 agar slant. One holding just 2 mg. of a bacterial growth is known 

 as a "Normaloese," or "Normal loop." To make these loops a little 

 apparatus consisting of a number of steel rods held in small wooden 

 blocks has been constructed. By winding the free end of the platinum 

 wire around the smallest steel rod a loop is formed which will just 

 hold 2 mg. ; the other steel rods form loops holding, respectively, 2, 

 5, and 10 mg. The quantity of bacterial growth removed from an 

 agar slant with such a "Normaloese" is well rubbed up with 2 c.c. of 

 physiologic salt solution and the entire mixture is injected. An animal 

 so treated is said to have received one, two, or five, as the case may be, 

 "Normaloesen" of a certain bacterial growth. 



Collodion Sacs. It is sometimes desirable to implant bacteria into 

 the body of an animal in such a manner that they are protected 

 against the phagocytes of that animal. This is done by the aid of 

 collodion sacs whose walls permit osmotic processes to continue but 

 prevent the emigration of bacteria and the entrance of leukocytes and 

 other cells. The simplest method for preparing them is as follows: 

 Clean a small test-tube and dry it completely by washing first in 

 absolute alcohol and then in ether. Pour some fairly thick collodion, 

 or celloidin as used in section work, into the dry tube and move it 

 continually in such a manner that the collodion coats its entire interior. 

 When the collodion becomes very thick in consequence of evaporation, 

 let the last few drops run over the rim at the mouth to the outside of 

 the tube. The tube is then filled with water, and after a little while 

 the outside collodion is peeled off without tearing it from its connection 

 with the inside collodion. The collodion surrounding the inner mouth 

 of the tube is loosened, and by allowing water from the faucet to flow 

 between it and the test-tube wall it gradually separates. A slight 

 pulling on the collodion is often necessary completely to detach it 

 from the tube. A glass tube slightly smaller than the test-tube is now 

 prepared, and near one end a narrow constriction is blown in over a 

 flame. About 1 J inches of the lower end of the collodion sac is now cut 

 off and the open end is slipped over the constricted glass tube and 

 fastened to it with a piece of good surgical silk. Finally, fresh thick 

 collodion is painted over the silk and the upper rim of the sac over 

 the glass tube, making a water-tight connection between the sac and 

 glass tube. Of course, each sac must be tested before it is slipped 

 over the glass tube. A number of them should be prepared, as only 



