IMMUNITY AND VACCINE THERAPY 483 



tuberculosis and glanders has not been generally successful. 

 The subject needs much additional investigation. 



Active and passive immunity. Most authors recognize 

 an active and a passive immunity. The active immunity in- 

 cludes those cases in which the specific antitoxin or immune 

 bodies (amboceptors) are produced within the body as a result 

 of the stimulation of the tissues by the antigen (either the 

 specific organism or its toxin). Thus a horse that recovers 

 from an attack of tetanus or has been made resistant to it by 

 repeated injections of tetanus toxin possesses an active im- 

 munity to tetanus. Passive immunity is where the individual 

 receives from without a sufficient quantity of antitoxin or 

 amboceptors with which to neutralize the toxin or destroy the 

 invading bacteria should they appear in the tissues. The 

 horse that receives a quantity of tetanus antitoxin is made 

 passively immune to the disease. As a rule active immunity 

 is of much longer duration than the passive variety. 



Immunity against protozoan diseases and filterable 

 viruses. The work on immunity has been largely in connec- 

 tion with bacterial diseases. Experimental work has shown, 

 however, that immunity can be established against several of 

 the protozoa. Whether the same classifications can be applied 

 here as in bacterial immunity is doubtful. Our knowledge of 

 the tissue response to protozoa is not sufficient to warrant the 

 discussion of the question. It is a fact, however, that cattle 

 can be made immune to Texas fever 1 by injecting subcu- 

 taneously from one to two cubic centimeters of the blood 

 serum or defibrinated blood of immune cattle. If the injection 

 is made in young calves and in cool weather the loss is very 

 slight. The work of de Schweinitz and Dorset 2 and others 

 has shown that immunity can be conferred against hog 



1 Schroeder. Report U. S. Bureau Animal Industry, 1898, p. 273. 

 Connaway. Bulletin No. 37, Mo. State Bd. of Agric., 1897. 

 Francis and Connaway. Bulletin No. 35, Texas Agric. Exper. 

 Station, 1899. 



- de Schweinitz and Dorset. Circular No. 41, U. S. Bureau of 

 Animal Industry, 1903. 



