68 Biology of Micro-organisms 



grows only at or below i8° to 2o°C., inoculation of about i per cent 

 of the body-weight with a liquid culture seven days old should bi 

 made into the dorsal lymph-sac of a frog. (2) When a speciei 

 grows at 25°C. and upward, an inoculation should be made into th( 

 peritoneal cavity of the most susceptible (in general) of warm- 

 blooded animals — i.e., the mouse, either the white or the ordinarj 

 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 wiU be successful 

 in causing the death of the mouse. If the inoculations of the frog 

 and mouse both prove negative, the committee think it unnecessary 

 to insist upon any further tests of pathogenesis as being requisite 

 for work in species differentiation. 



Production of Enzymes.- — Some of these have already been men- 

 tioned as causing fermentation and putrefaction, coagulating milk, 

 dissolving gelatin, etc. There are, however, others which have 

 interesting and important actions upon both animal and vegetable 

 substances. 



Emmerich and Low* observed that in old cultures of Bacillus 

 pyocyaneus the bacteria become transformed into a gelatinous mass, 

 and were led to experiment with old and degenerating cultures con- 

 densed to J^o volume in a vacuum apparatus. The bacteriolytic 

 powers were then found to be much increased, and they were sub- 

 sequently able to precipitate from the concentrated culture an 

 enzyme, which they called pyocyanase. The authors reached the 

 rather hasty conclusions that the cessation of growth of bacteria in 

 cultures depends upon the generation of enz5Tnes; 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 fiir Hygiene," iSgg. 



