POPULAR SCIENCE 105 



When meat is preserved by freezing the case is quite 

 different. It is stated that if the meat is frozen to — io° C. 

 the growth of bacteria is absolutely prevented, since this cannot 

 take place in a solid medium, while the chemical actions pro- 

 ceed at a negligible rate. Hence, frozen meat can be kept 

 without deterioration for a much longer time than in the chilled 

 condition ; frozen beef can be kept for three years, or even 

 more, without reduction in its nutritive value. 



The physical changes taking place in freezing are those 

 connected with the water relations of the tissue. As is well 

 known from the appearance of frozen meat, water which was 

 formerly bound in some way becomes free. This is particu- 

 larly the case with beef, in which the amount of water lost 

 under certain circumstances can be very considerable. For 

 instance, Ascoli and Silvestri ' mention a loss of 15 to 20 per 

 cent, of the fresh weight of the meat. The juice which runs 

 out contains valuable nutritive substances ! and the quantities 

 which can be lost in this way may be very considerable. The 

 keeping qualities after thawing may be much reduced by this 

 behaviour. Nevertheless, Gautier ■ found the composition of 

 frozen meat the same as that of fresh meat, or that it even had 

 a higher nutritive value on account of the water loss. As re- 

 gards beef this process is to some extent reversible if careful 

 thawing be applied. 4 



It seems very desirable to have an official gradation of 

 frozen meat based on such an essential property as this binding 

 of water. 



In the concluding article we shall deal with the question 

 as to the conditions under which these irreversible changes in 

 regard to water relations can be minimised or avoided. 



1 See summary in Le Froid, Paris, Jan. 1914. 



1 W. Storp, JJber Gefrierfleisch, Verbffentlichen aus d. Gebiete d. Militar- 

 Sanitatswesens, Heft 55; Arbeiten aus d. hyg.-chem. Untersuckungsstellen, VI 

 Teil, 51-73, Berlin, 1913. 



' A. Gautier, U Alimentation et les regimes chez Vhomme sain et chez les 

 ma/ades, Deuxieme Edition, Paris, 1904. See also Richardson and Scherubel, 

 "The Deterioration and Commercial Preservation of Flesh Foods," Journ. Amer. 

 Chem. Soc. 30, 1515-64, 1908. 



4 W. D. Richardson, " The Cold Storage of Beef and Poultry," Premier 

 Congres International du Froid, Rapports et Communications, vol. ii. pp. 261-316, 

 Paris, 1908. 



(To be concluded) 



