194 A MANUAL OF BACTERIOLOGY 



drops counted in the second determination will be greater than in 

 the first. 1 



ANTI-FERMENTS. 2 By the injection of rennin or other enzyme 

 the blood-serum of the treated animal acquires the property of 

 neutralising the action of the enzyme with which the inoculation 

 has been performed. Thus if rennin and anti -rennin (the serum of 

 an animal injected with rennin) be mixed with milk no curdling 

 takes place. Similarly, the serum of an animal inoculated with 

 pancreatin inhibits the action of this ferment, and if coagulated 

 egg-albumen, pancreatin, and anti -pancreatin be mixed, the egg- 

 albumen undergoes no digestion. 



PnECiPiTiNS. 3 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 microbes. 

 If to such a filtrate in a test-tube a little of the corresponding 

 anti -serum be added by running in carefully, so that it forms a layer 

 at the bottom, an opalescent ring makes its appearance at the line 

 of junction of the two fluids. So also if an animal be injected with 

 milk, its serum, when added to milk of the same kind as that with 

 which it has been injected, causes precipitation of the casein. This 

 reaction is specific, and it is thus possible to distinguish various 

 milks from one another. Similarly, anti-sera which produce pre- 

 cipitates, each with the homologous substance, are obtained by 

 the injection of peptone, of egg-albumen, blood-serum, and other 

 proteins. The latter reaction has an important medico-legal 

 application, for by means of it the blood and flesh of different 

 species of animals can be distinguished. Thus the presence of 

 horseflesh in sausages can be detected. The method employed is 

 to inject a rabbit intraperitoneally with four to six injections of 

 defibrinated blood or of blood-serum (or with a solution of the 

 particular substance, e.g. horseflesh), commencing with about 5 c.c. 

 and increasing to 10 c.c. at intervals of a few days. After treat- 

 ment the animal is bled from an ear vein, and the serum is obtained. 

 The blood to be tested may be dried on filter-paper, pieces are then 

 cut up, a solution is made in 1-6 per cent, sodium chloride solution, 

 and to this the specific serum is added. Tested in this way human 

 blood anti-serum reacts i.e. forms a precipitate markedly with 



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



2 See Dean, Trans. Path. Soc. Lond., vol. lii, 1901, Part 2, p. 127. 



3 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 disease). 



