44 BIOLOGY AND TECHNIQUE 



teriaJ cell, but in some cases may be closely bound to the cell-body and 

 separable only by extraction after death. In such cases they are spoken 

 of as endoenzymes. Whenever they are true secretory products, however, 

 they can be obtained separate from the microorganisms which form them 

 by filtration through a Berkefeld candle. From such nitrates they may, 

 in some cases, be obtained in the dry state by precipitation with alcohol. 

 When obtained in this way the precipitated enzyme is usually much 

 more thermostable than when in solution, for while soluble enzymes in 

 nitrates are usually destroyed by 70 C., and even less, the dried powder 

 may occasionally withstand 140 C. for as long as ten minutes. 1 



Apart from the general conditions of temperature and moisture, the 

 development of these enzymes seems to depend directly upon the presence 

 of proteids in the culture media. The number of bacterial species 

 which produce proteciytic enzymes is legion. Among those more com- 

 monly met with are staphylococci, B. subtilis, B. proteus, B. fsecalis 

 liquefaciens, Spirillum cholerae asiaticae, B. anthracis, B. tetani, B. pyo- 

 cyaneus, and a large number of others. The inability of any given micro- 

 organism to liquefy gelatin or fibrin by no means entirely excludes the 

 formation by it of proteolytic enzymes, since these ferments may often 

 be active for one particular class of proteid only. 



In order to study the qualitative and quantitative powers of any 

 given bacterial proteolyzing enzyme or protease, it is; of course, neces- 

 sary to study these processes in pure culture in the test tube with media 

 of known composition. In the refuse heap, in sewage, or in rotting 

 excreta, the process is an extremely complicated one, for besides the 

 bacteria which attack the proteid molecule itself, there are many other 

 species supplementing these and each other, one species attacking the 

 more or less complex end-products left by the action of the others. 



Exactly what the chemical reactions are which take place in these 

 cleavages is not entirely clear. It is believed, however, that most of the 

 cleavages are of an hydrolytic nature. 



In general, the action of the proteid-splitting ferments is comparable 

 to that of the pancreatic ferment trypsin, and they are most often active 

 in an alkaline environment. They differ, among themselves, chiefly in 

 the form of proteid which 'they are competent to attack, and in the 

 extent to which they are able to reduce it toward its simple radicles. 



A distinction is occasionally made between the terms putrefaction 

 and decay, the former being used to refer to the decomposition taking 



1 Futvrimann, " Die Bakterienzyme/' p. 46. 



