394 MILK AND THE PUBLIC HEALTH CHAP. 



bacteria, and the resulting powder is almost sterile. Tubercle 

 bacilli appear to be killed. For example, Hoffmann l tested 

 whether the Just-Hatmaker method would kill tubercle bacilli. 

 He introduced tubercle bacilli into the liquid milk, and found 

 that none remained alive in the dried milk, as shown by 

 guinea-pig inoculation tests. 



Both these methods of preserving milk are special pro- 

 cedures, and, as such, not comparable to the methods of pre- 

 servation described above. The conversion of the milk into 

 a tinned form, whether as a dry powder or a syrup, costs 

 money, so that economically they are more expensive than 

 milk. 



These methods may be useful for special purposes, but can- 

 not be practically applied to the milk supply generally, while, 

 if practicable, their extended use would be undesirable on public 

 health grounds. 



Reconstructed Milk. Dr. Buchanan, 2 in his Eeport on 

 Foods, etc., to the Local Government Board, draws attention to 

 the existence of a process for reconstructing milk after separa- 

 tion and concentration, which has lately been employed on a 

 commercial scale at an establishment near London. 



In this process, which is said to have considerable vogue in 

 New York and other American cities, milk is separated, and the 

 separated milk concentrated in a specially constructed receptacle at 

 140 F. (60 C.), while a current of filtered air is passed through 

 the liquid. By concentration for 2J hours to 3 hours the separ- 

 ated milk is reduced to about one-fifth of its original volume. 

 The cream is also exposed, for about an hour, to similar treatment. 

 The concentrated separated milk and the cream are then despatched 

 by road or rail to a town depot, at which they are mixed in any 

 desired proportion with boiled tap water, and distributed in bulk or 

 in bottles. 



At the establishment in question, this reconstructed milk was 

 stated always to contain at least 3*25 per cent of milk fat. Analysis 

 of several samples confirmed this statement, and also the claim of 

 the producers that, in consequence of the low temperature of con- 

 centration, enzymes are retained which are natural to raw milk but 

 are destroyed in ordinary processes of pasteurising. On the other 

 hand, bacteriological tests failed to confirm the claims of the pro- 

 ducers that the milk was exceptionally free from bacteria, and that 



1 Archivf. Hygiene, 1906, vol. lix. p. 216. 

 2 Report of Medical Officer, Local Government Board, 1909-10, p. 211. 



