44 MADRAS FISHERIES BULLETIN VOL. XIV^ 



qualities provided the frozen fish was absolutely fresh when 

 treated. The reason for this great and vitally important difference 

 is the mechanical effects caused within the cells and tissues of an 

 animal (or a plant) by lowering the temperature to some point 

 below freezing point (a fish does not freeze at 32* F. because of the 

 saline constituents in the fluids and tissues). The effects are 

 particularly marked in the case of muscle fibres and this is the 

 economic fact of importance to us, for the edible parts of a fish are 

 the great muscles that form the flesh of the body. These muscles 

 are made up of extremely fine fibres, consisting of a delicate 

 sheath enclosing stiff semi-gelatinous contents of highly complex 

 chemical composition. It has been ascertained by microscopical 

 and other means, that when such animal structures be subjected to 

 temperature below that of the freezing point of water, the water 

 contained within the thick semi-gelatinous contents of the fibre 

 sheath, tends to separate out, gathering into drops which tend to 

 run together to form large ones and to pass eventually through the 

 sheath into the spaces between the fibres ; this process goes on till 

 the protoplasmic mass becomes honeycombed and converted into 

 a shrivelled sponge-like frame-work. If the temperature be suffici- 

 ently low, the exuded water freezes and changes into ice crystals. 

 The alteration thus produced are twofold — chemical and physical. 

 The former consists principally in the separation of an essential 

 compound, water, from the protoi^lasm of the cells (fibres), and its 

 exudation into the spaces between ; this if carried far enough 

 definitely destroys the protoplasm; it dies, and as a consequence 

 post-mortem change, autolysis it is called, becomes very rapid in 

 thawed tissues altered in the way I have described by slow freezing. 

 Among other chemical changes that ensue from autolysis, is one 

 that is found to affect antl destroy any particular flavour inherent 

 in the flesh. 



The physical change is more easily understood. It is common 

 knowledge that water expands on freezing and that the more 

 slowly freezing takes place the larger are the ice crystals produced. 

 Consider then the disruptive effect on closely packed muscle fibres 

 of the formation around them and within them of large ice crystals : 

 on a microscopic scale the same mechanical effect is taking place 

 that we see when a water-pipe bursts during frosty weather. 



If, however, freezing takes place with great celerity as in the 

 case of brine-freezing and we have seen that its rapidity is as 15 to 



