553 GENERAL THERAPEUTIC MEASURES 



DIAGNOSTIC PRODUCTS.- 



There is a class of very important biologic products which for the 

 present^ though not of therapeutic value^ are being used as diagnostic 

 agents in the control of diseases. It is a known fact that the entrance 

 of an infection into the animal organism always has a stimulating effect 

 upon the production of anti-bodies ; the appearance of anti-bodies in the 

 system is an indication of a struggle against the infection. As a result 

 of the struggle the body shows either an increased or diminished re- 

 sistance against the infection; an increased resistance being manifested 

 as immunity, and a decreased resistance as hyper-susceptibility. This 

 state of hypersensitiveness toward the infection or its products may, in 

 some diseases, be utilized for diagnostic purposes. Thus, for instance, 

 an animal affected with glanders or tuberculosis will develop a hyper- 

 sensitiveness to the respective products of the germs, that is, to inallein 

 or tuberculin, and the injection of such products into infected animals 

 will result in a general or local reaction, manifesting itself by a rise of 

 temperature, systemic disturbance, and local swelling at the point of 

 inoculation. 



Investigations have also established that such reactions may be in- 

 duced in various ways, thus according to the method of application they 

 are known as subcutaneous, ophthalmic, intradermal, intrapalpebral, and 

 cutaneous tests. The underlying principle in all these tests is the same 

 in that it is aimed to utilize the hypersensitive state of an infected animal, 

 to respond to the introduction of the respective antigen in visible or 

 otherwise determinable manifestations. In the subcutaneous test we 

 thereby obtain a typical rise in temperature associated with more or less 

 systemic disturbance; in the ophthalmic test infected animals respond 

 with a purulent conjunctivitis; in the intradermal test we obtain a pro- 

 nounced infiltration. 



Diagnosis of Tuberculosis. 



The relative value of the various tests has been studied carefully, 

 and for the present time in tuberculosis the subcutaneous test has to be 

 given first place, although the intradermal method is also being recog- 

 nized as quite accurate and dependable. The intradermal test is less 

 expensive in time and labor, but its application and interpretation requires 

 considerable skill and experience. Both the intradermal and ophthalmic 

 test for the diagnosis of tuberculosis may be used as supplementary to the 

 thermic test. 



Tuberculin is prepared by cultivating tubercle bacilli in a five per 

 cent, glycerin bouillon for six to eight weeks at 37° C, whereupon the 

 tubercle bacilli are killed by boiling and the bouillon is then freed from 

 the killed bacilli by filtration. The concentration of the filtrate containing 

 the tuberculin to 0.1 of its original volume represents what is known as 

 Koch's "old tuberculin." 



The subcutaneous tuberculin as marketed at the present time is 

 either rediluted Koch's old tuberculin or the original filtrate without 

 concentration of which one mil represents a definite amount of Koch's 

 old tuberculin. It is required by the Bureau of Animal Industry that a 

 dose of subcutaneous tuberculin should contain not less than 0.5 grams 

 of Koch's old tuberculin and manufacturers are instructed to designate 



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