76 



The so frequently praised microscopical examination is of little 

 value unless it be for the determination of foreign substances, as 

 blood, pus, colostrum, detritus, etc., or solid adulterants. For the 

 determination of the percentage of fat, it is without value, though 

 it is correct, that a milk shows the butter globules in all the sizes 

 as they are recognized to occur in normal milk, but further apart, 

 when it had simply been watered. The want of the larger and 

 medium-sized globules may indicate skimming, since the larger 

 globules are known to rise sooner and easier. They are the iirst 

 to form the cream, and disappear, therefore, with the removal of 

 this first-formed cream. 



The greatest difficulty exists in getting uniform samples for 

 microscopical examination, as was first shown by Conrad, who has 

 proved that, in examining woman's milk, even the same sample, 

 carefully mixed and sampled by an arrangement to control the 

 quantity taken for one slide, will give results showing differences 

 in number, size and distribution of the fat globules. The methods 

 used for estimating the number of globules are, moreover, arbi- 

 trary and uncertain. We will later on give a more satisfactory 

 method for the determination of fat. 



Determination of Specific Gravity. 



The specific gravity of milk depends upon three points : The 

 substances, as milk sugar, salts and albuminates, dissolved or con- 

 tained in the water whicli forms part of the milk, in a diffused, 

 gelatinous condition, increase the specific gravity, while the sus- 

 pended fat globules diminish it. Increase of temperature dimin- 

 ishes the specific gravity likewise, while decrease of temperature 

 will increase it. The specific gravity is determined, for practical 

 purposes, with sufficient accuracy, by the use of a milk areometer, 

 the so-called lactodensimeter. 



It should be remarked here that the name lactometer, ;\hich 

 has been given to these instruments, is wrong, and should cer- 

 tainly not be used by scientifically educated persons. It conveys 

 a wrong impression ; for, to this day, we have no instrument, and 

 least in the lactodensimeter, which furnishes us a direct measure 

 for the quality of the milk. 



The best and most exact instruments are those of Quevenne, 

 the inventor of the lactodensimeter, which give, in abbreviated 



