MODIFIED MILK AND MILK PRODUCTS 113 



Care must be taken to thoroughly cleanse and sterilize the 

 outside of the tin before opening, while the instrument to open 

 the tin, which may conveniently be an ordinary tin-opener, must 

 be sterilized before use. 



The fact that condensed milk is a culture medium for 

 bacteria although not a very suitable one is of much greater 

 importance than the fact that it contains a few bacteria. The 

 latter fact is evidently of no public health significance. 



II. Dried Milk. 



Dried milk is now manufactured commercially to a con- 

 siderable extent. It is the powder obtained either by passing 

 milk rapidly between heated surfaces so that it is deprived of 

 its water, or by drying on a cylinder in a partial vacuum. 

 This dry powder, on being again mixed with water, is converted 

 into a fluid which looks like milk, and which, on ordinary 

 chemical analysis, shows the chemical constituents of that sub- 

 stance. In other respects considerable alterations have taken 

 place, for example the enzymes have been destroyed, the fat 

 globules physically altered, etc. 



To examine bacteriologically the dried milk would have to 

 be dissolved in sterile water, and the mixture examined by 

 methods similar to those employed for milk. 



The chief examinations which might be required would be 

 to determine if sterile, or if not the number and kinds of 

 bacteria present, and also to ascertain if tubercle bacilli were 

 present. 



From the limited number of experiments which have been 

 made it appears that tubercle bacilli are killed in the process of 

 manufacture. 



III. Cream. 



The bacteriological examination of cream is of considerable 

 importance, since it is usually richer in bacteria than either 

 whole milk or separated milk. This is shown by direct bacterial 

 examinations, while in guinea-pig inoculation experiments it is 

 not uncommon to find that a considerably higher percentage 



s. w. 8 



