TEXT-BOOK OF BACTERIOLOGY. 283 



may be changed into vaccines by keeping- them in the steam steril- 

 izer for about half an hour at 100 C., thus destroying- the existing 

 germs, 



Cultures treated in this manner show, according to their age, a 

 very different degree of virulence. Those of about twenty days in 

 quantities of 2 to 3 c.cm. kill Guinea-pigs after injection into the 

 subcutaneous cellular tissue or the abdominal cavity, while those 

 of about five days are still borne in doses of 5 c.cm. In the former 

 case (as in the inoculation of living bacteria) a rapid fall of the body 

 temperature, far below the normal limit, is perceptible; death takes 

 place after twenty -four to forty-eight hours; dissection exhibits es- 

 pecial^ a somewhat slow pathological process and a very consid- 

 erable fatty degeneration of the liver. In the latter case a fall of 

 temperature after a few hours occurs at first, but it rises very soon 

 to a feverish reaction. This lasts about a day, after which time the 

 animals will soon recover, and have then acquired immunity. This 

 does not, indeed, directly follow inoculation. As a rule one or two 

 weeks will elapse before complete success is attained i.e., before 

 the virulent material (for instance, the vibrionic blood of a pigeon 

 perishing after infection with virulent bacteria) is taken in doses of 

 1 to 2 c.cm. without causing the death of the animals. Arise of the 

 body temperature, lasting several days, and local changes (such as 

 the appearance of a tolerably extensive oedema at the inoculation 

 spot) indicate that the artificially-immunized body feels at least 

 the invasion of the bacteria. 



The nature and composition of the really efficient substance are, 

 as yet, not exactly known. It is striking that the toxic cultures 

 possess a very high degree of alkalescence and lose their virulence, 

 and hence their vaccinating power (as Pfeiffer states), by neutrali- 

 zation with sulphuric acid, but not by treatment with muriatic acid. 



The experiments concerning the production of artificial immu- 

 nity with the vibrio Metschnikoff are especially interesting because 

 the discoverer of this micro-organism, Gamaleia, is inclined to trans- 

 fer the observations and experiences he made, in an almost com- 

 pletely unchanged form, to Koch's vibrio of cholera asiatica; he 

 pretends to have reached similar results especially as regards pro- 

 tective inoculation. 



By repeated passages through the pigeon's body the comma 

 bacilli are thus said to assume an extremely high degree of viru- 

 lence; injection of sterilized cultures is said to render the animals 

 secure even against this most infectious matter; and thus a "pre- 

 ventive inoculation " is said to have been found " against cholera 

 asiatica." The granting of immunity against cholera bacteria is 



