ZOOLOGY, ENTOMOLOGY, AND MEDICINE 239 



leukocytes and foreign material in the blood stream, and when 

 this attraction takes place as was demonstrated with the iron 

 filings, it is called a positive chemotaxis. Numerous other 

 observers realized that when an invasion of bacteria into a 

 body had taken place successfully that some of the phagocytic 

 cells had lost their power of eating, and destroying bacterias. 

 This phagocytic power of the body being lessened, the power 

 of the bacteria was increased, and the body was then in a 

 diseased condition. In the accounts of Robert Koch we read 

 that he took pure cultures of living micro organisms, and 

 after introducing them into normal salt solution, killed them 

 with heat, and injected them into a body that was not resistant 

 to the disease produced by the micro organisms used. It was 

 then claimed that after repeated injections, these animals 

 would be inoculated with the disease, due to the fact that 

 phagocytes had been injected by the invasion of dead bacteria. 



This led up to the wonderful theory of Metchnikoff, which 

 has continued to the present day. In 1883 Metchnikoff first 

 claimed that phagocytes protected the higher animals against 

 infection by disease producing bacteria, although for years 

 he knew of the presence of phagocytes in lower animals, in the 

 class of "Tunicata" called "Actinia." His experiments on high- 

 er animals were quite easy to be carried out. 



By defibrinating the blood of a goose, by whipping it with a 

 bundle of pieces of wood or wire he obtained a mixture of 

 blood corpuscles and serum, (the fibrin was removed by the 

 whipping) this defibrinated blood was mixed with physiolog- 

 ical salt solution, centrifuged and the clear supernatant fluid 

 pipetted off. In this way he obtained what is now known as 

 "washed red blood corpuscles." A few cubic centimeters of 

 these washed red blood corpuscles were suspended in physio- 

 logical salt solution and were injected into the peritoneal cav- 

 ity of a guinea pig. and after a short time removed from the 

 peritoneum together with the exudate from the abdominal 

 cavity with which they had been mixed. He found that the 

 exudate contained numerous large mononuclear white blood 

 corpuscles of the guinea pig, and that these contained many red 

 blood corpuscles of the goose. Then at short intervals of time he 

 removed more exudate for examination and found the goose 



