52 ADAPTATION AND DISEASE 



And we can easily demonstrate the fact, either within the 

 body itself or in the test-tube. Take the peritoneal fluid of 

 a normal untreated guinea-pig and introduce cholera spirilla 

 into it, and they will immediately begin to multiply. Take 

 another guinea-pig and inoculate it subcutaneously with minute 

 doses of dead cholera spirilla at intervals of a few days, gradually 

 increasing the amount inoculated, and follow this by repeated 

 inoculations of live cholera spirilla ; and now either (a) withdraw 

 some of the peritoneal fluid of the highly immunized guinea-pig 

 and add to a drop of this a suspension of living cholera spirilla, 

 or (6) inject living spirilla direct into the peritoneal cavity, and 

 with a pipette withdraw from time to time a drop of the peritoneal 

 fluid and examine under the microscope, or even (c) take a normal 

 guinea-pig, inject into it five or ten times the fatal dose of cholera 

 spirilla and follow this by injecting, also intraperitoneally, 1 

 or 2 c.cm. of the blood serum of the immunized guinea-pig and 

 from time to time remove a drop of fluid from the peritoneal 

 cavity and examine under the microscope, preferably in each 

 case upon the warm stage. Whichever means of experiment is 

 employed, it is seen that the spirilla lose their motility, swell 

 up, become rounded, then become progressively smaller, and, as 

 Pfeiffer (to whom we owe the reaction) expresses it, they undergo 

 solution " like sugar in water." Any member of this group of 

 pathogenic microbes may be selected with like results. 

 RadziewsM, 1 for example, has observed the phenomenon with 

 B. typhosus, B. pyocyaneus, B. pneumoniae, Streptococcus pyo- 

 genes, and Bacillus anthracis. Clearly in the process of im- 

 munization the tissues of the body, or certain of them, have 

 gained the property of elaborating bacteriolytic ferments, or 

 substances which digest and dissolve the bacterial bodies — sub- 

 stances not present in the untreated or control animals, and 

 coincidently the treated animal becomes immunized, becomes 

 capable of withstanding and destroying, with little or no general 

 reaction or bodily disturbance, many times what otherwise 

 would be a surely fatal dose. And here is the striking fact : 

 this reaction is in general narrowly specific, so narrowly specific 

 that it is employed by the German School to distinguish between, 

 for example, closely related species of spirilla. If a guinea-pig 

 be inoculated with the cholera spirilla from man, its body fluids 

 1 Zeitachr. f. Hygiene, xxxvii., 1901, 1. 



