910 EXPERIMENT STATION KEOOKO. 



))a<'UTia ill milk when I'rcsli ami ;it a later [icriod, Id ilctcrmim' w lictlirr strainiiiji; 

 throujih clu'i'sc cloth exerts an inllueiice upon (lie bactc-rial i'<inteiit of the milk, to 

 study the relation between the number of bacteria and the development of acid, and 

 to study the effect of a chaiijie in tenii)erature upon tlu^ total number of bacteria and 

 the relative number of the different tyjies. The milk was obtained from one cow in 

 the ordinary manner, and stnune<l and unstrained samples were kept at temperatures 

 of 50 and 70°. 



Some of the general conclusions <lrawn from the taliulated data are suniiiiari/,e(l 

 below: 



The examination of the fresh milk showed that straining through cheese cloth had 

 only a slight effect in removing bacteria, which was considered somewhat suqirising, 

 inasmuch as previous experiments had shown that straining in this manner removed 

 about 40 per cent of the dirt present. Of the l)acteria removed by straining the 

 larger percentage consisted of nonacid sjiecies, although the results as a whole 

 showed very little difference. The relative proportion of the acid and nonai-id bac- 

 teria in fresh milk was, however, considered of little importance as regards the 

 rapidity of curdling, inasmuch as the type of lactic-acid bacteria originally ])resent 

 was replaced in most cases by the end of 50 hours by Bacicrinin hu-tlx nrvVi. 



The examination of the milk kept for 50 hours at 70° showed that the strained 

 samples contained on the whole a slightly larger nmnber of bacteria than the 

 unstrained samples. Neither the total number of bacteria nor the jiercentage of 

 lactic-acid liacteria was l)elieved to l)e influenced to any api)recial)le extent by 

 straining. In cases where the acid l)acteria had reached 99 jier cent of the tota,l 

 number of bacteria present the acidity of the milk was not very greatly increased, 

 indicating that the production of acid takes i)lace rapidly only after the acid liactcria 

 have gained full control. The development of acid bacteria was unaffecte(l by 

 straining. In general, samples containing the larger number of acid liacteria also 

 contained the highest percentage of acid. 



The examination of milk kei)t for 50 hours at 50° showed a striking reduction in 

 the number of bacteria as com2:)ared with the milk kept at 70°, the average number 

 in the samples kept at 70° being neai-ly 500,000,000 and at 50°, 0,000,000. The acid 

 bacteria were reduced in greater proportion than the total bacteria. The strained 

 samples contained slightly larger nnmliers of acid bacteria than the unstrained sam- 

 ples, although the difference was considered too slight to have any meaning. There 

 Avas practically no increase in the acidity of the milk, the average acidity being a])out 

 0.20 jier cent, while that of the original samjjles averaged 0.18 per cent. 



At 70° the time required for curdling was 87 and 97 hours, while at 50° the average 

 was about 300 hours, the unstrained samples keejnng on an average about 10 hours 

 longer than the strained samples. The time of curdling at 50° appeared to be 

 unrelated to the total number of bacteria present at the outset. The conclusion is 

 drawn that for practical purposes the temperature is of more imjiortance in the keep- 

 ing of milk than the original 1 )acterial c-ontamination. The number of 1 lacteria jiresent 

 at the time of curdling varied from 282,000,000 to 1,059,000,000. The acidity also 

 showed considerable variations. 



Aseptic milk, H. W. Conn and W. A. Stocking, Jr. ( Cunnedirul Stuvn< hiUi. Rpl. 

 1903, pp. 5^-62). — This series of experiments, which is in continuation of the two 

 series noted above, was designed to compare ordinary milk with milk obtained inider 

 exceptional precautions and here called aseptic milk. The precautions taken included 

 the washing of the udder and flanks of the cow with a 3 per cent solution of boric acid 

 and wiping with a sterilized cloth, the milker also washing his hands with the same 

 solution and wijiing them on a sterilized cloth. After the milking was half done 

 these precautions were rejieated, and milk was drawn into a sterilized covered pail 

 through 4 thicknesses of sterilized cheese cloth and a layer of absorljent cotton and 

 sanii)led for bacteriological examination. All the experiments were made with the 



