ANTI-FERMENTS 237 



tion of a highly agglutinating serum. After incubating for four 

 hours, the mixture is centrifuged, the clear supernatant fluid 

 decanted, and the agglutinating power of the decanted liquid is 

 then tested on the organism with which the serum was prepared. 

 If the organism tested is homologous with the organism with 

 which the agglutinating serum was prepared, the decanted fluid 

 will have lost most, or a considerable proportion, of its agglutinat- 

 ing power for the latter. 



THE MEIOSTAGMIN KEACTION. Ascoli found that if an immune 

 serum be mixed with an alcoholic extract of the homologous 

 antigen and the mixture incubated at 37 C. for two hours the 

 surface tension is reduced ; if the serum and antigen extract are 

 not homologous the surface tension is unaltered. For example, 

 in the case of typhoid the following is the procedure. An alcoholic 

 extract of typhoid bacilli is prepared ; this is diluted with saline 

 solution to 1-1,0001-1,000,000. The typhoid serum is simi- 

 larly diluted, 1-10. To 9 c.c. of the diluted serum 1 c.c. of the 

 diluted antigen extract is added. By means of some form of 

 viscosimeter or stalagmometer the number of drops yielded by a 

 given volume of the mixture is ascertained, immediately after the 

 mixture is made, and after the mixture has been incubated at 

 37 C. for two hours. If the surface tension has been reduced, 

 the number of drops counted in the second determination will be 

 greater than in the first. 1 



ANTI-FERMENTS. It has been stated in the past that injection 

 of an enzyme, e.g. rennin, is followed by the development of anti- 

 enzyme which inhibits the action of the enzyme with which it 

 was produced. Thus if rennin and antirennin (the serum of an 

 animal injected with rennin) be mixed with milk no curdling 

 takes place. Considerable doubt has, however, been cast of late 

 on the production of anti-enzyme. 



PRECIPITINS. 2 Kraus was the first to demonstrate the presence 

 of specific precipitins in blood by adding typhoid, cholera, and 

 plague anti-sera to filtrates of the cultures of the corresponding 



1 Ascoli and Izar, Munch, med. Woch., Ivii, 1910, pp. 62, 182, 403. 



2 See Nuttall, Journ. of Hyg., vol. i, 1901, p. 367 (Bibliog.), also Brit. Med. 

 Journ., 1902, vol. i, p. 825 ; Welsh and Chapman, Journ. of Hygiene, vol. x, 

 1910, p. 177 ; ibid., Australasian Med. Gazette, December 12, 1908 (hydatid 



