THE AGGLUTINATION TKST. 421 



inoculating- witli graduall}' increasing closes of the organism at 

 intervals of a week or so for a long period. 



Agglutinins are often found in milk and tears, therefore 

 they are probably got rid of in the excretions. Tlieir actual 

 seat of production in the animal body is not yet known, but it 

 has been noted by various observers that they are found at an 

 early date after injection in the lymphoid tissues, such as the 

 spleen. Removal of the spleen, however, j;loes n.ot in any way 

 affect their ])roduction, and an extract of leucocytes does not 

 afford any agglutinin at all. 



No agglutination of bacteria by a scrum will take ]:)lace in 

 the absence of salts, though combination takes place as with 

 agglutinoid. Sodium chloride is the usual salt used, though 

 other salts may and have been used. .'^odium chloride solution 

 in a strength of 0.8 per cent, is always used, as it has been 

 found that this is the amount present in normal serum. Tubercle 

 bacilli in 0.8 per cent, salt solution will occasionally agglutinate 

 spontaneously in the absence of serum, but by reducing tlie salt 

 content to o.i per cent, this can be avoided. Certain non- 

 specific substances such as i : 1,000 corrosive sublimate solution, 

 hydrogen peroxide, various stains, such as fuchsin and safranin, 

 can cause agglutination in an emidsion of bacteria >\hich closely 

 resembles that ])roduced by a serum. 



We can now go on to a discussion of the various theories 

 put forward at one time or another to explain the mechanism 

 of agglutination of bacteria. A similar phenomenon ma\- be 

 observed in a suspension of small particles of clay in water to 

 which a little salt is added. The particles run together and 

 commence to sediment, leaving the water clear. The same 

 phenomenon has lieen put forward to explain the formation 

 of mud-banks at the mouths of rivers, where the fresh and salt 

 water meet. With bacteria, however, agglutination, except in 

 the spontaneous cases previously mentioned, is always a result 

 of the addition to them of an agglutinating serum. 



Gniber thought that agglutinin caused the enveloi)es of the 

 bacteria to become sticky, so that they adhered together. This 

 theory explains why bacteria which have once comejn contact 

 with each other stick together, but fails to explain why they 

 approacli each other, and also does not take into account the 

 possible fact that the phenomenon is in part physical. 



Nicolle thought that the agglutinin precipitated the agglutin- 

 able material in the bacteria, causing them to become swollen 

 and viscous in the outer cover, and thus to adhere to each other. 

 This theory is essentially similar to ( iruber's, and has the same 

 faults. 



Palta!<f considered that agglutination of bacteria was due 

 to their being drawn into the interstices of a coagulum. No 

 such coagulum has ever 1)een demonstrated, as it easily could 

 be if i)resent. by staining a preparation of the agglutinated 

 bacteria. 



