VII. QUICK-FREEZING AND FREEZING-DRYING 217 



ether, petroleum ether, alcohol, and similar liquid solvents. De- 

 naturation of the proteins on such extraction is greatly reduced as 

 compared to extraction of liquid products. Various proteins may be 

 freeze-dried simply for preservation during the course of an investiga- 

 tion. For example, many enzymes have been dried without loss in 

 activity (2). Crystalline beef liver catalase has been dried; the 

 properties of the dried product compared to those of undried crystal- 

 line beef liver catalase. Bounce and Rowland (23) report that the 

 dried material is not crystallizable. 



Guinea pig serum may be preserved with no loss in complementary 

 activity over a period of years, even with storage at room tempera- 

 ture, in contrast with loss of up to 50% in activity on storage over- 

 night at 5°C. as a liquid. Diagnostic laboratories and research lab- 

 oratories may gain the benefit of uniform complement obtained from 

 a pool of blood from a large number of animals even though only 

 small quantities are used at a time. By preparing such a large pool 

 and freeze-drying it in small containers, the product is available as 

 required. 



Many other biological products have been dried successfully in the 

 frozen state with no change in properties and with the final products 

 having excellent characteristics of solubiUty. Teague, Galbraith, 

 Hummel, Williams, and Macy report that the removal of water from 

 feces, urine, and milk by dehydration in vacuo from the frozen state 

 permits indefinite preservation of the dry material in an undenatured 

 form if stored under proper conditions (20). This method of dehy- 

 dration has many advantages over oven drying. Oven drying, at 

 70°C. and under, hydrolyzes the soaps in feces, causing exaggerated 

 values for the free fatty acids and a reduction in the soaps, although 

 the total free fatty acid plus soap values are the same for both methods 

 of drying. The nitrogen contents of the Cryochem samples of feCes, 

 urine, and milk approximate those of fresh specimens. In obtaining 

 energy data by the bomb calorimeter, the Cryochem-dried material 

 permits greater accuracy in analyses and economy of time and ma- 

 terials by eliminating one nitrogen determination and the correction 

 for nitrogen loss in drying. 



Bile has been prepared in dry form, so that a stable product may be 

 stored ready to dissolve for use in obstructive jaundice. It is believed 

 that the abnormal bleeding that occurs is due to the failure of the 

 absorption of vitamin K in the absence of bile in the intestines (21). 



Farr and Hiller have reported on the successful drying of heme- 



