PROTEOLYTIC ENZYMES. 299 



either abolished, or at least reduced to a minimum, in order to 

 prevent the formation of decomposition products that are not only 

 useless to the body, but even troublesome and dangerous. As a 

 matter of fact, GEORGE NUTTAL and H. THIERFELDER (I.) recently 

 afforded a convincing proof of Nencki's theory by rearing some 

 young porpoises, born by the aid of the Csesarean operation, and 

 nourished in a suitable sterilised chamber. On examination at 

 the close of the experiment, they were found perfectly healthy, 

 though entirely free from bacteria. Pasteur's assumption (which 

 was also supported by Soxhlet with reference to his incomplete 

 process of milk sterilising) was thus shown to be erroneous. A 

 few observations on this point were also made by E. DUCLAUX (XL). 



170. Proteolytic Enzymes. 



All the fission fungi (with the few exceptions given in Chapter 

 xxxiii.) require nitrogenous nutriment for the construction of their 

 cells. Such of these nitrogenous materials as are soluble in water, 

 and therefore diffusible through the cell-wall by osmosis, need not 

 be referred to here. Mostly, however, the nutriment presented to 

 the bacteria is insoluble in water, and this is particularly the case 

 with the protein albuminoids. To enable these latter to supply 

 the nitrogen required for the elaboration of the bacterial plasma 

 they must first be converted into soluble compounds, a task which 

 is effected by the proteolytic enzymes. So far no comprehensive 

 study of these active bacterial secretions has been made, and at 

 present our knowledge is chiefly confined to the enzymes dissolving 

 gelatin and fibrin. A new classification of the bacteria into two 

 groups, the liquefactive and non-liquefactive towards gelatin, 

 according to the presence or absence of a proteolytic enzyme, has 

 obtained currency in practical bacteriology since the introduction 

 of the Koch system of plate-cultures. 



We are indebted to CL. FERMI (II.) for the first extensive 

 series of pure culture investigations on this point. He proved 

 that a gelatin-dissolving enzyme is formed in cultures of the 

 following species of Schizomycetes : Bacillus subtilis, B. anthracis, 

 B. megatherium, B. pyocyaneus, Vibrio cholerce asiaticce, Vibrio 

 FinTder-Prior, Micrococcus prodigiosus, M. ascoformis, M. ramosus, 

 spirilla from cheese, &c. Fibrin is dissolved as well as gelatin, 

 but less readily that the latter. Egg-albumin and coagulated 

 blood-serum offer greater resistance to these bacteria, thus indicat- 

 ing that pepsin is not present. Reasons exist for assuming that 

 the enzymes produced by the said microbes are not all of the same 

 kind, one conclusive indication being afforded by their behaviour 

 under different temperatures. Thus, for example, the proteolytic 

 enzyme produced by Micrococcus prodigiosus is rendered inactive 

 (in solution) by a temperature of 55 C., that from B. pyocyaneus 

 by 60 C., that from B. anthracis by 65 C., and that from Vibrio 



