162 PRINCIPLES OF VETERINARY SURGERY 



the blood is called phagolysis. Metchnikoff states that be- 

 sides the cytase, another substance exists in the blood which 

 attaches itself to the bacterial cell and renders it susceptible 

 to the action of the cytase. This he designates by the name 

 of fixative. The fixative and cytase are both soluble fer- 

 ments, but can easily be differentiated. The cytase is 

 destroyed by heating at SS"' C, while the fixative is de- 

 stroyed by heating 60° or 65° C. The fixatives are dif- 

 ferentiated by a high specificity never observed in cytase, in 

 that the majority of them are not capable of attaching them- 

 selves to more than one species of bacteria or to one class 

 of animal cells. The microcytase, on the other hand, can 

 attack all kinds of micro-organis'ms and the macrocytase 

 all kinds of animal cells. As to the origin of this fixative 

 (the amboceptor of Ehrlich) Metchnikoff believes that it 

 comes from the phagocytes. It is involved in antibacterial 

 immunity. 



The fixatives and cytases are not the only soluble fer- 

 ments which appear in the fluids of immunized animals, 

 The serum is often characterized by another distinct prop- 

 erty which Metchnikofif designates the protective substance. 

 This substance resists higher heating than any of the other 

 ferments, even to 70° C. Under this temperature a protec- 

 tive serum loses its bactericidal power, if this is present, 

 but will prevent infection when injected into another ani- 

 mal, — Asiatic cholera, for example. Similarly, normal 

 serums contain no fixatives, but they are protective. On 

 the other hand the fixative may be present in serums which 

 are not protective, and still further, not every immune 

 serum will protect other animals when injected into them. 

 Very often there are found agglutinative substances in im- 

 mune serums. These resist the same temperatures as the 

 fixatives, and are characterized by the same Specificity, but 

 a slight agglutinative property may be associated with a 



