104 ACTIVITIES OF BACTERIA. 



sera. If an animal has recovered from an infection with one 

 of these diseases, or has received in a proper manner the 

 devitalized cause of the disease, then its body, especially 

 its blood, contains materials which even in high dilutions 

 possess intense and even specific destructive action upon 

 the micro-organisms concerned. Also in man suffering 

 from the infectious diseases such bactericidal bodies de- 

 velop in the blood; indeed, they are often present from the 

 eighth to the fourteenth day of the disease, and may per- 

 sist after recovery for weeks, months, or even years. An 

 active immunity of this kind has been successfully pro- 

 duced in man against cholera and pest. In these diseases 

 a positive immunity is conferred by the injection of devi- 

 talized culture masses (Ferran and Hafkine). 



The bactericidal serum from animals actively immun- 

 ized to a high degree has been employed with good results 

 to produce passive immunity in other organisms in various 

 diseases (for example, swine erysipelas by Emmerich). 

 Usually there is injected, besides the serum, also the normal 

 or attenuated specific agent. ^ 



To obtain serum one proceeds as follows: 



1. Collection of human serum. The finger is carefully 

 cleansed with soap and water, alcohol and ether, and a 

 small puncture is made with a strong needle on the front 

 and to the side at the end of the finger, so that three or 

 four large drops of blood are obtained. The blood is col- 

 lected in a U-shaped capillary tube, and the ends closed 

 with wax or sealing-wax. As soon as possible the sample 

 is centrifugated in a high-speed hand centrifuge, the wax 

 being previously removed and the open ends of the tube 

 being turned toward the center. The centrifugation is 

 continued for ten minutes. After it is completed each 

 limb of the tube contains about 1 to 1.5 cm. of clear serum. 

 A piece 1 cm. long is now measured off in each branch and, 

 after marking it lightly with a file scratch, the tube is 



' In mouth and foot disease, for example, Loffler, for the purpose of 

 producing immunity, injected a mixture of serum from the recovered 

 animal together with the virulent contents of the vesicle of the sick 

 animal. KoUe, in immunizing against murrain, employs the simul- 

 taneous injection (in two diiierent places) of serum from a recovered 

 cow, and virulent blood from the diseased animal. 



