MILK. 179 



however, frequently remains suspended in the milk, in conse- 

 quence of its retaining a number of butter globules, which 

 lessen its specific gravity. Soon, however, other changes 

 show themselves, still more indicative of putrefaction: the 

 layer of cream swells up, becomes more yellow, and a fungus 

 springs up upon its surface, the Penicillum glaucum. This at 

 first presents the appearance of white velvet ; but afterwards 

 as soon as the fungus has reached the period of fructification 

 it assumes a green colour. 



The idea of M. Turpin, that this fungus had its origin in, 

 and was developed from, the milk globule, scarcely requires 

 a serious refutation. 



At the same time the odour of the milk undergoes a com- 

 plete change : sweet when it is fresh, it becomes acid as it 

 decomposes, and gives out more especially the smell of 

 cheese. 



Examined with the microscope, in addition to the fungus 

 alluded to above, numerous infusory animalcules will likewise 

 be detected. 



Now the changes above described, and which are expe- 

 rienced by the milk of every animal, will be more clearly un- 

 derstood if the milk be previously filtered, and the butter and 

 the serum being obtained separately, those alterations which 

 ensue in each be noticed. 



It will be observed, that it is the butter, or non azotised 

 substance, which undergoes the acid fermentation, and on 

 which the fungi are principally and most generally developed. 



The serum, on the contrary, becomes alkaline and exhibits 

 the ammoniacal or putrid fermentation, this depending upon 

 the azotised principle which it holds in solution, viz. the 

 cheese. 



It will be remarked, also, that the serum in changing does 

 not exhibit the striking odour of cheese which the milk itself 

 gives 'out under the same circumstances, and from which it 

 may be concluded, that a certain amount of butter is neces- 

 sary to produce the peculiar smell of cheese. 



The phenomena to which the putrefaction of milk give 

 rise result, then, from two kinds of fermentation ; the acid, in 



