76 ESSENTIALS OF BACTERIOLOGY. 



slight degree, but during infection produces lysins specific for 

 the germ in question. 



Agglutinins. These are bodies formed in the blood-serum in 

 response to the stimulation of certain bacteria, such as the 

 typhoid bacillus, Bacillus coli communis, Micrococcus meli- 

 tensis, the bacillus of dysentery, the cholera spirillum, etc. 

 When such a serum is added to cultures of the particular 

 organism concerned, the bacteria become clumped in motion- 

 less masses. A modified form of agglutination in which long 

 strings of bacteria are formed is known as the " thread " reac- 

 tion. 



Precipitins. Animals immunized to certain bacteria or to 

 albumins of different sorts form bodies which cause the blood- 

 serum to give a precipitate when added to cultures of these 

 organisms or fluids containing the specific albumen. The 

 phenomenon has found forensic application in the identifica- 

 tion of blood-stains. 



CHAPTER XV. 



EXPERIMENTS UPON ANIMALS. 



THE smaller rodents and birds are the ones usually employed 

 for inoculation, as rabbits, Guinea-pigs, rats and mice, and 

 pigeons, and chickens ; sometimes monkeys. These are pre- 

 ferred, because easily acted upon by the various bacteria, readily 

 obtained, and not expensive. 



The white mouse is very prolific and easily kept, and is there- 

 fore a favorite animal for experiment. It lives well upon a little 

 moistened bread. A small box, perforated with holes, is filled 

 partly with sawdust, and in this ten to twelve mice can be kept. 

 When the female becomes pregnant she should be removed to 

 a glass jar until the young have opened their eyes, because the 

 males, which have not been raised together, are apt to attack- 

 each other. 



Guinea-pigs. When Guinea-pigs have plenty of light and 

 air they multiply rapidly. Therefore it is best to have them in 



