PRINCIPLKS OF VETERINARY SURGERY 175 



The "opsonic power or index" represents the relation 

 between the phagocytic power of an animal and that of a 

 normal animal of the same species. It is obtained by mix- 

 ing a little of the animal's serum with washed leucocytes 

 and a few bacteria, and determining from a stained speci- 

 men of the mixture after it has been incubated at 37° C for 

 15 minutes, the average number of bacteria per leucocyte 

 ingested, which may be ten, twenty, etc. Staphylococci per 

 leucocyte in the presence of a normal serum for man equals 

 twenty. If that of a given serum say is fifteen, then the 

 opsonic power would be 15-20 or ^ of normal. The nor- 

 mal index varies in different animals. 



The pathological value of a low and high index has not 

 as yet been worked out. A low index has been observed, 

 however, at the beginning of pneumonia, while at the crisis 

 it may rise as high as 1.6. 



There are many other interesting bodies which have en- 

 tered into the explanation of immunity, such as anti-anti- 

 bodies, cytotoxins, auto-antibodies, iso-antibodies, toxids, 

 toxons, etc. For an understanding of these, the reader must 

 be referred to a more complete work on the subject of im- 

 munity. 



From the foregoing, it will be seen that the explanation 

 of immunity while yet a theory, has too many practical fea- 

 tures for the veterinarian to ignore it. 



As to the structure and action of toxin and antitoxin, 

 they have proved to be chemical bodies of definite action. 

 Antitoxin can be introduced into an animal without produc- 

 ing any harm. Also, if portions of toxin and antitoxin are 

 mixed together in a test-tube, and inoculated into the body, 

 no harm results. Thus it will be seen that antitoxin com- 

 bines with toxin in a test-tube as well as in the body. 



