BACTERIA IN ARTICLES OF FOOD. 589 



cies of sarcina, Staphylococcus pyogenes aureus, and other pus cocci. 

 Usually coagulation is due to the combined action of several bacteria, 

 among which Bacillus acidi lactici is apt to be the most prominent. 



Other bacteria produce coagulation without the lactic acid fer- 

 mentation. This appears to be due to the formation of a soluble 

 ferment which acts like rennet, causing the coagulation of milk 

 which has a neutral or slightly alkaline reaction. The coagu- 

 lated casein in this case is subsequently redissolved. The bacteria 

 which produce this change for the most part form spores, while the 

 lactic acid ferments do not. If, therefore, milk is heated nearly to the 

 boiling point the acid-forming bacteria will be destroyed and the 

 spores of the other species surviving will give rise to coagulation 

 without the production of lactic acid. Among the more common 

 microorganisms of this group are the Bacillus butyricus (Hueppe), 

 Bacillus mesentericus vulgatus, Loffler's " white milk-bacillus," and 

 the bacilli described by Duclaux under the generic name of Tyrothrix. 



Other fermentations are produced by certain chromogenic bacteria, 

 and these, as a rule, are not as harmless from a sanitary point of view 

 as those above referred to. Blue milk is produced by the presence of 

 Bacillus cyanogenus, yellow milk by Bacillus synxanthus (Schroter) 

 and by a species obtained by List from the faeces of a sheep and 

 another found by Adametz in cheese. The well-known Bacillus 

 prodigiosus produces its characteristic red pigment when present in 

 milk, and a bluish-red color is caused by Bacterium lactis erythrogenes 

 (Hueppe). 



Viscous fermentation in milk is produced by several different bac- 

 teria, among others by a micrococcus studied by Schmidt-Muhlheim, 

 and a short bacillus isolated by Adametz Bacillus lactis viscosus. 

 Milk which has undergone this change is unwholesome as food ; it 

 is recognized by the long filaments which are produced when it is 

 touched with any object and this is slowly withdrawn. 



The Caucasian milk ferment, Bacillus Caucasicus, produces a 

 special fermentation, which has been referred to in Section IV. , Part 

 Second (page 132). 



Various pathogenic bacteria have occasionally been found in milk 

 in addition to the tubercle bacillus already referred to. Thus Adametz 

 found Staphylococcus pyogenes aureus in two samples which had 

 been submitted to him for examination, one of which had given rise 

 to vomiting and diarrhoea. Wyssokowitsch cultivated from milk 

 which had been standing some time a pathogenic bacillus, named by 

 him Bacillus oxytocus perniciosus. 



The special microorganism which produces the poisonous pto- 

 maine called by Vaughan tyrotoxicon has not yet been isolated ; nor 

 do we know the exact cause of scarlet fever, although there is evi- 



