124 M. bumas on the Constitution of Milk and Blood. 



An inverse test leads to the same conclusions. A neutral 

 salt, such as sulphate of soda, added to milk, enables us to 

 filter it, and to retain upon the filter the globules of butter, 

 whilst the serosity flows off perfectly limpid and clear. If the 

 washings with saline water be continued, these globules may 

 be freed from all the soluble products of the serum. Now if 

 the butter consisted of simple fatty globules, there would then 

 remain with them no trace of albuminous or caseous matter. 

 But whatever care may be taken to prolong the washings, we 

 always find with the fatty matter such a proportion of albu- 

 minized substance that there can be no doubt that it has 

 remained there in the form of those envelopes or cells which 

 constitute the globules of butter. 



The microscope, moreover, shows plainly the constitution 

 of the globules of butter, and reveals the constant presence of 

 the envelopes. It is sufiicient to crush the globules of milk 

 by means of the compressor, to obtain a conviction that, after 

 the spreading of the fatty matter, the butter-cell still retains its 

 form and outline, thus showing that the contents and the con- 

 tainer have each their distinct existence. 



For these reasons, and for many others (for no conscientious 

 chemist can assert that the analysis of milk has made known 

 all the products necessary to life which that aliment contains), 

 we must renounce, for the present, the pretension to make 

 milk, and especially abstain from assimilating any emulsions 

 to this product. 



Besides we cannot have too much reserve where we have to 

 pronounce upon the identity of two products, one natm'al, the 

 other artificial, if they are not crystallizable or volatile — that is 

 to say, definite. We can never afiirm that we have repro- 

 duced a mineral water, or sea-water for example. When 

 manure for plants, or aliments for man and animals are in 

 question, is not the same reserve still more imperative ? 



These indefinite natm'al mixtures contain substances which 

 the coarsest analysis discovers, with others less strongly cha- 

 racterized or less abundant, which are only revealed by deli- 

 cate chemistry, and others again, and perhaps the most essen- 

 tial, which still escape us, either because they exist in infi- 

 nitesimal proportions, or because they belong to the category 

 of bodies which have not hitherto been distinguished from 

 other chemical species. 



It is therefore always prudent to abstain from pronouncing 

 upon the identity of these indefinite mixtures employed in the 

 sustenance of life, in which the smallest and most insignificant 

 traces of matters may prove to be not only efficacious, but 

 even indispensable. In proportion as science extends her 



