IMMUNITV. 



83 



is produced in an animal either in iitero or after birth, and may 

 be active, or passive, bacterial or toxic. 



Acti'Z'c acquired immunity is, no doubt, the result of cellu- 

 lar action and may be produced as follows: — 



1. By an animal becoming- infected and reco\'erino; frnm an 

 attack of the disease, e. g. blackleg. 



2. By inoculation of a susceptible animal with a small 

 cpiantitv of the \-irulent causative microparasites, thus produc- 

 ing the disease in a mild form. This is practiced in immunizing 

 cattle against tick fever. 



Fig. 61. — Deniodex FolIiciiI<»riim, 



vai;et>- Canis 

 Field showing- various slagos of 

 develt.tpnitnt, 



a. Ova. 



b. Pupa. 



c. Adult. 



d. A piceu of Scab. 



Fi^. 61a. — I>eni<nlex I-oIli<'ijl<)ruin. 



variety Cauls. 

 Adult Male, magnified i"0 timis 

 showini,' wide liead. ^^■llh ii.y- 

 trum. short hss < .^. artleles each J 

 2 claws and eionijatcd body. 



3. Bv inoculating a susceptible animal with an attenuated 

 virus, (vaccine.) Htirscs, mules, cattle, and sheep are immun- 

 ized to anthrax by a vaccine. 



4. Bv repeated inoculations of a susceptible animal with 

 small quantities of a tnxin of a specific pathogenic microparasite. 

 tetanus toxin or other active poison as snake venom. This 

 method is used only in the production of antitoxins or in inimun- 

 izincr animals against zootoxins and phytotoxins. 



