240 PHARMACEUTICAL BACTERIOLOGY 



of the body against bacterial invasion. This observation by Metchnikoff, 

 fully verified by others, is generally known as the phagocyte theory and the 

 phenomenon is designated phagocytosis. The principle involved in 

 phagocytic activity is well illustrated in the lesser local injuries, as cuts, 

 bruises, abrasions, etc. Normally such injuries are always infected by 

 various germs of the environment, as the several varieties of pus microbes. 

 These invading microbes at once begin their attack upon the tissue cells 

 and blood-corpuscles. The leucocytes which are present begin to feed 

 upon the rapidly multiplying pus organisms but for a time, as a rule, the 

 latter have the upper hand and as a result there is perceptible pus forma- 

 tion ("the laudable pus" of older writers) represented by dead leucocytes 

 gorged with microbes. As the inflammatory reaction becomes more 

 marked, indicated by redness and swelling of the tissues immediately about 

 the injury; increased numbers of leucocytes (phagocytes) are brought to 

 the scene of action and gradually they gain control until finally the invad- 

 ing microbes are all destroyed, thus permitting a rapid and unhindered 

 restoring of tissue cells, recognized as the healing process. This phago- 

 cytic action is entirely distinct from the action of antitoxins and lysins, and 

 the three are potent factors in immunity. 



The investigations of Metchnikoff and Leishman on phagocytosis 

 paved the way for the discovery of opsonins by Wright. It was noticed 

 that the phagocytic activity was influenced by conditions to be found out- 

 side of the leucocytes themselves. Metchnikoff held that the principal 

 part is played by substances found in the serum and in the tissue cells to 

 which he gave the name " stimulins." The purpose of these substances in 

 the tissue fluids have not yet been satisfactorily demonstrated, but 

 Metchnikoff considers their function to be that of acting upon the phago- 

 cytes in such a manner as to stimulate them to perform phagocytosis. 

 Wright, Hektoen, Neufeld and others have demonstrated beyond doubt, 

 the presence in the blood of substances which act upon the infecting bac- 

 teria and get them ready for the completion of their destruction by the 

 phagocytes. To these bodies Wright gave the name " opsonins" (Latin, 

 opsono, I prepare for). That opsonins are not formed in the blood is cer- 

 tain. Experimental evidence seems to prove that they are products of 

 muscular or subcutaneous cellular activity. It is probable that the actual 

 formation of opsonin occurs in the muscle tissues and passes thence to the 

 blood. Wright has demonstrated more or less satisfactorily the presence 

 of opsonins in the blood of animals and humans and by a special technic 

 has measured the relative amount. This measurement is a ratio of the 

 activity of the phagocytes in normal blood and of that in disease, before 

 and after stimulation, determined by the number of bacteria that a single 

 phagocyte will ingest the so-called opsonic index. This index or ratio is 



