METHODS OF SERO-DIAGNOSIS. 213 



many regard the reaction to tuberculin and mallein as being 

 capable of explanation on similar lines. 



There are still some other methods to which attention must 

 be paid. One of these is a method of diagnosis lately described 

 by Forgeot and Caesari and used by them in the diagnosis of 

 ulcerative lymphangitis of the horse. This disease is due to 

 infection by the Preisz-Nocard bacillus, an organism which is 

 also responsible for the production of Caseous pneumonia and 

 Caseous lymphadenitis in sheep, as well as certain abscesses in 

 the lungs of calves. The technique they employ is to inject the 

 serum of the subject for examination into the gastrocnemius 

 muscles of a guinea-pig and on the following day this animal is 

 injected subcutaneously with a solution containing the Preiss- 

 Nocard bacilli, which have been killed and extracted with a mix- 

 ture of alcohol and ether. 



Two control animals are inoculated at the same time. One 

 of these receives an injection of the bacilli alone and the other 

 is inoculated in the same manner as the test animal, but receives 

 an injection of normal horse serum in place of the subject's 

 serum. If the subject for examination is affected with the disease, 

 then the guinea-pig inoculated with the bacilli and the serum of 

 the subject shows no local reaction at the site of injection of the 

 bacilli extract or, at most, only a minimal scar formation, whilst 

 the control animals should die proving the toxic effect of the 

 bacilli extract. 



Another method we might mention is that suggested by cer- 

 tain workers who have thought it possible to utilize, in the 

 diagnosis of cancer, the isolysins which are present in the blood 

 of certain individuals affected with this disease. The percentage 

 of successes with this method in human medicine is, however, 

 not very high and appears to be even less when the test has been 

 used in the case of some of the domestic animals. 



There is a method, however, which has been introduced bv 

 Ascoli and Izar which has given very encouraging results in 

 diagnosis, especially in the case of malignant tumours and epizoo- 

 tic aphtha (foot-and-mouth disease), and in the human subject, 

 in the case of syphilis, malignant tumours, echinococcosis, and 

 some other diseases. This method is the so-called " Meiostagmin- 

 reaction," which depends on the fact, that when a serum con- 

 taining a specific antibody is brought in contact with a solution 

 of its respective antigen, and the mixture is kept at 37 C for 

 two hours or 50 C for one hour, there occurs a decrease in the 

 surface tension of the mixture of the two solutions, and this 

 decrease of surface tension may be measured by estimating the 

 number of drops formed when the liquid is dropped from a 

 Traube's stalagmometer. This number is compared with the 

 number, obtained in a similar manner, but using a normal serum 

 mixed with the antigen, and by thus estimating the difference in 

 surface tension between the two liquids one may arrive at a 

 diagnosis. 



This concludes our review of the methods of sero-diagnosn 

 applicable to diseases of stock in South Africa, and it is to be 



