GENERAL TECHNIC 67 



2. No fixed rules as to the amount to be injected can be given. 

 Experience may show a general method to be the most successful, but 

 as previously mentioned, the general condition and reaction of the ani- 

 mal will be the main guide as to the amount and frequency of the in- 

 jections. Severe reactions may yield unsuccessful results, and doses 

 so small as apparently to give no reaction may lead to a high-grade im- 

 munity. 



3. A single injection seldom yields a highly valent serum. Re- 

 peated inoculations are usually necessary, and may be given in the fol- 

 lowing way: 



(a) A small dose of antigen is injected. If a reaction sets in, wait 

 until this has subsided, and then, after the fifth day, make a second in- 

 jection of a somewhat larger dose. After another interval of from five 

 to seven days a third injection of a still larger dosage is administered, 

 and so on for two or more injections. 



(b) Same as preceding method, except that the first dose is the max- 

 imum one; subsequent injections are of decreasing amounts. 



(c) Same as preceding, with a constant dose of antigen at each in- 

 jection which does not produce a severe reaction. 



(d) For several successive days a small or medium-sized dose of 

 antigen is injected (Gay). 



The first three methods give excellent results, and the third is es- 

 pecially useful when a serum is needed as soon as possible. 



4. It must be emphasized that good results are largely dependent on 

 the care with which the animals are injected. The operator should work 

 as aseptically as possible, especially when giving intraperitoneal and 

 intravenous injections, and avoid the production of embolism by the 

 injection of air or solid particles. Give the injections slowly, and take 

 particular care of the animals. However carefully the injections may 

 be given, unsatisfactory results not infrequently occur. Either the 

 animal refuses to react with the production of antibodies, or dies just 

 when immunization is about completed. It is, therefore, good practice 

 to immunize more than one rabbit at one sitting, in order that immune 

 serum may be had at the time planned. 



; Antigens. Animals may be actively immunized with the following 

 substances : 



1. With soluble bacterial toxins, as in the manufacture of antitoxins. 



2. With bacteria themselves; whether living, attenuated, or dead, 

 as in making bacterial agglutinins, precipitins, immune opsonins, and 

 lysins (bacteriolysins) . 



