58 Biology of Bacteria 



i. e., the mouse, either the white or the ordinary house 

 mouse. The inoculation should consist of about i per cent, 

 of the body-weight of the mouse of a four- to eight-hour 

 standard bouillon culture, or a broth or water suspension 

 of one platinum loop from solid cultures. When such 

 intraperitoneal injection fails, it is unlikely that other 

 methods of inoculation will be successful in causing the 

 death of the mouse. If the inoculations of the frog and 

 mouse both prove negative, the committee think it un- 

 necessary to insist upon any further tests of pathogenesis 

 as being requisite for work in species differentiation. 



Production of Enzymes by Bacteria. Some of these 

 have already been mentioned as causing fermentation and 

 putrefaction, coagulating milk, dissolving gelatin, etc. 

 There are, however, others which have interesting and im- 

 portant actions upon both animal and vegetable substances. 



Knowledge upon the subject is just becoming systema- 

 tized, one of the best writings being by Emmerich and 

 Low,* who observed that in old cultures of Bacillus pyo- 

 cyaneus the bacteria become transformed into a gelatinous 

 mass, and were led to experiment with old and degener- 

 ating cultures condensed to -fa volume in a vacuum appa- 

 ratus. The bacteriolytic powers were then found to be 

 much increased, and they were subsequently able to precipi- 

 tate from the concentrated culture an enzyme, which they 

 called pyocyanase. The authors reach the rather hasty con- 

 clusions that the cessation of growth of bacteria in cultures 

 depends upon the generation of enzymes ; that the enzymes 

 destroy the dead bacteria; that the enzymes will kill and 

 dissolve living bacteria and destroy toxins, and, therefore, 

 are useful for the treatment of infectious diseases; and 

 that antitoxins are simply accumulated enzymes which the 

 immunized animals have received during treatment, and 

 which, appearing in the serum, produce the effects so well 

 known. 



It is probable that many of the toxic effects of bacteria 

 and their cultures depend upon enzymic substances, the 

 nature of which we do not yet understand. 



* " Zeitschrift fur Hygiene," 1899. 



