LAB-PRODUCING BACTERIA. 243 



following paragraph. For industrial purposes, however, there is 

 only a single source (the richest) worthy of consideration, viz., the 

 stomach of the calf. The method of production indicated above is 

 now practised on a manufacturing scale, especially in Copenhagen, 

 whence most of the German and Dutch cheese factories derive 

 their supplies. The products are : Rennet solution, containing 

 boracic acid to improve the keeping quality ; rennet powder, and 

 finally, rennet tabloids. The efficacy and germ-content of these 

 preparations were investigated by FRITZ BAUMANX (I.). 



146. Lab-Producing Bacteria. 



Milk may also curdle without previous acidification or addition 

 of rennet. HAUBNER (I.) in 1852 was the first to record this fact, 

 and the first explanatory research was made by DUCLAUX (IX.) in 

 1882. From his studies in this matter the latter concluded that 

 this precipitation of casein (occurring with an alkaline reaction) is 

 due to the activity of certain bacteria which excrete an enzyme 

 resembling lab; and CONN (III.), in 1892, succeeded in isolating 

 this enzyme from cultures of such Schizomycetes. At first sight 

 the identity of this lab with the active ingredient in the rennet 

 solution from the stomach of the calf appears probable, but the 

 discovery that the bacteria in question (which include many of the 

 species belonging to the potato bacillus group, in) are able to 

 -coagulate boiled sterilised milk, goes against this view, rennet being 

 incapable of producing this reaction. 



The presence or absence of this power affords, in many instances, 

 a valuable means of differentiation between two species of bacteria. 

 This is particularly the case with the organism producing abdominal 

 typhus in man, viz.. Bacillus typhi abdominalis, discovered by Eberth 

 in 1880, and already referred to in preceding chapters. This 

 microbe is not endowed with the faculty in question, whereas, as 

 JAK. URY (I.) has shown, a number of the putrefactive bacteria 

 collectively termed Bacterium coli commune, and greatly resembling 

 the typhus bacillus in form, &c., rapidly produce coagulation in 

 milk. According to the researches of C. GORINI (I. and II.), Micro- 

 coccus prodigiosus also produces this enzyme in large quantities. 



147. Casease. 



Not infrequently the precipitation of casein effected by such 

 bacteria disappears again after a short time. Duclaux ascertained 

 that this new alteration is due to a second (albumin-dissolving) 

 nzyme, to which he gave the name of casease. The same observer 

 also discovered, in the case of several species of Tyrothrix isolated 

 from Cantal cheese, and of which a description will be found in 

 Chapter xxxi., certain bacteria gifted with the faculty of excret- 

 ing both enzymes, the casein precipitant and the casein solvent. 



