132 Edwin O. Jordan 



the reaction of the culture medium. It is probable that the reaction 

 is of importance only in so far as it influences the general conditions 

 of growth of the microorganism. The facts to be adduced presently 

 concerning the conditions under which the enzymes manifest their 

 activity tend to support this view. 



PHYSICAL CHARACTERS. 



Resistance of gelatinases to heat. — The statements of authors are 

 not in harmony on this point. Fermi' found that the gelatinolytic 

 enzymes were destroyed at relatively low temperatures : the majority 

 of those tested by him were rendered inactive at 5o°-55° C, and all 

 were destroyed at 7o°C. Abbott and Gildersleeve,^ on the other 

 hand, observed a surprising heat resistance on the part of the proteo- 

 lyitc enzymes elaborated by certain species, and asserted that some 

 were even "capable of exhibiting their characteristic function after 

 exposure in the moist state to a temperature of 100° C. for 15 to 30 

 minutes." Hata^ also declares that the enzymes of B. prodigiosus 

 and B. fluorescens liq. resist high temperatures. None of these 

 authors have given definite data concerning the amount and strength 

 of the enzymes employed in their experiments. 



The varying results obtained in some of my earlier work gave rise 

 to the suspicion that differences in the reaction of the medium in 

 which the enzyme was contained were responsible, at least in part, for 

 the divergent statements. It has been pointed out elsewhere in this 

 paper that the reaction of the culture medium is often profoundly 

 affected by bacterial growth, that gelatin cultures of liquefying species 

 are more acid than the corresponding broth cultures, and that the 

 reaction varies according to the particular stage of growth and enzyme 

 action at which it is tested. The influence of the reaction of the 

 medium (presence of H or OH ions) upon the thermal death-point of 

 the enzyme is shown in the experiments which follow. It is unneces- 

 sary further to multiply such instances. In almost every case tested 

 it was found that increasing the acidity of the enzyme-containing 

 fluid raised the " heat resistance" of the enzyme, while adding to 

 the alkalinity lowered it. In one case the M. L. D. of an enzyme 

 (o.oi c.c, B. prodigiosus) was not affected by boiling for 15 minutes 



' Centralbl. f. Bakt., 1891, 10, p. 401. ' Cenlralbl. f. Bakt., 1904, Ref. 34, p. 308. 



• Jour. Med. Res., 1903, s, p. 42. 



