Till-: ag(;luti.\ati!jn test. 41^ 



of time required varies greatly with the particular organism and 

 the strength of the antiserum. The deposit in complete agglu- 

 tination is (juite typical as compared with an ordinary deposit 

 of organisms. In the latter case the deposit is round and well- 

 defined, occupying the least possible space, and when examined 

 under the microscope the organisms will be fomid to be packed 

 neatly together. In the former case the deposit resembles 

 either a thin veil with waving edges or an irregular star-shaped 

 mass, and on microscopical examination the organisms appear 

 to be lying in disordered masses as if they have suddenly been 

 thrown together without any attempt at arrangement. In a 

 hanging-drop preparation, which is made by placing a drop of 

 the culture and its antiserum on a cover-sli]) and inverting it 

 over a slide with a well in it, one can watch the whole process 

 of agglutination under the microscope. In this case one notices 

 first that the organisms, if motile, lose their motility, and then 

 run slowly into masses, leaving the intervening fluid quite clear. 



Other cells l)esides bacteria may be agglutinated, and it 

 has been found that fresh cattle serum possesses the power of 

 strongly agglutinating the red blood cor]:)Uscles of various 'other 

 animals, though these agglutinated corpuscles usually after- 

 wards undergo haemolysis, that is 1^0 say, they are destroyed and 

 their hremoglobin liberated. .Sheep's blood corpuscles are 

 agglutinated Ijut not haeniolysed by fresh cattle serum. It i^ 

 not intended in this paper to describe any agglutinins except 

 those which are produced b\ Inicterial infection, as the agglu- 

 tination of red corpuscles is a study in itself. 



Speaking generally, the reaction of agglutination is specific, 

 and the antiserum against the tyi)hoid bacillus will not clump the 

 cholera or Malta fever organisms, and the serttm of a cow 

 infected with contagious abortion will not cUunp the glanders 

 bacillus, etc. (irottp reactions with closely allied species of 

 bacteria do, how^ever, occur, a case in point being the agglutina- 

 tion of tvi)hoid and also paratyphoid bacilli by the .same anti- 

 senun. The difficulty in such a case can be overcome by using 

 very dilute antiserum, as it has been found that the anti-typhoid 

 serum will agglutinate typhoid bacilli when diluted 80 or more 

 times, whereas it will not agglutinate paratyphoid bacilli when 

 diluted more than at most 50 times. These grouj:) reactions are 

 very useful in the classification of bacterial species, and have 

 added much further evidence to that previously obtained by 

 comparison of size, special staining reactions, appearance of 

 growth in particular media, etc. 



Bacteria which have been acted on by an agglutinating 

 serum are not in any wav altered either in appearance or viru- 

 lence. What the actual benefit the animal receives by agglu- 

 tinating invading bacteria is not known, but it has been thought 

 that by being rendered immobile they are made a more easy 

 prey for leucocytes, though it has been noted that ingestion of 

 bacteria or phagocytosis may be almost absent in a disease 



