EXPERIMENT STATION BULLETINS. 



295 



The only conclusion that can be drawn from germs 120, 122, 123, 125, 126, 129, 130, 

 132 and 133 is that the acidity produced must be in part due to the conditions under 

 which they were grown. I find this further proved by the use of hydrogen in place of 

 carbon dioxide, although the results differ. 



XXV. HOW HYDROGEN MAY ALTER THE ACIDITY OF MILK CULTURES OF SPECIFIC 



MICRO-ORGANISMS. 



Here again we find that the acidity varies when the micro-organisms in question 

 are grown under hydrogen but not exactly in the same way as carbon dioxide. The 

 methods employed were identical with those used in studying the influences of carbon 

 dioxide. The following table will indicate the influence of hydrogen: — 



TABLE XXII. 



HYDROGEN ANAEROBIC CONDITIONS AS COMPARED WITH AEROBIC CONDITIONS 



REGARDING THE ACIDITY PRODUCED. 



No. of micro-organism. 



Acidity of air cultures 



Acidity of hydrogen cultures. 



No. of micro-organism 



Acidity of air cultures 



Acidity of hydrogen cultures. 



126. 



.57(1 

 .706 



Con- 

 trol. 



.162 

 .162 



XXVI. IS IT THE CARBON DIOXIDE WHICH CAUSES A CONSTANT RISE OF ACIDITY 

 IN CONFINED MILK IN CONTRA-DISTINCTION TO MILK EXPOSED TO THE AIR? 



In this test, tubes were completely filled with milk, plugged so as to exclude all air. 

 and the stoppered ends were placed in mercury. The milk used was from a sample 

 obtained immediately after milking. The tubes and stoppers were sterile. Some of the 

 same sample was placed in a Fernbach flask so as to form a layer 1 cm. thick. The 

 acidity of the milk was 16° or .144 per cent (estimated as lactic acid). The milk 

 remained confined and also exposed for 16 hours. The summary of the work is as 

 follows : 



Milk confined for 16 hours gave 16° (.144 per cent) acidity. 

 Milk exposed for 16 hours gave 13.5° (.1215 per cent) acidity. (In tin vessel.) 

 Confined milk run drop by drop over six foot tin surface gave 14.5° (.1305 per 

 cent) acidity, a reduction of 1.5° (.0135 per cent) in the acidity. 



Confined milk brought to a brisk boil gave 14.5° (.1305 per cent) acidity, a 

 reduction of 1.5° (.0135 per cent) in the acidity. 

 Here we have an indication that carbon dioxide accounts for at least 1.5° acidity, 

 consequently a study of the acidity in confined milk without the influence of any gas 

 has been undertaken. 



XXVII. INFLUENCE OF CONFINEMENT OF MILK UPON ACIDITY. 



The milk samples of these tests, the results of which are given in tabulated form, 

 were, in each case, carried out in exactly the same manner as in the preceding experi- 

 ment; that is, the milk confined and also that exposed to the air came from the same lot 

 which was procured immediately after milking. In no instance was air allowed to 

 remain in the tubes. If we go back and recall the gas-content of milk as found to 

 exist immediately after milking the percentage of carbon dioxide would be about 

 sixty. If carbon dioxide in the free state is the determining factor then there should 

 exist corresponding results in acidity, likewise in the number of germs involved in the 

 fermentation. 



