The effects of spray-drying on the viability of fungous spores.

Much effort has been devoted recently to means of conserving viability by reducing the activity of cells through the withdrawal of water. Chief of these methods of desiccation is the lyophil or freeze-drying technique. The rationale behind freeze-drying is the supposition that water can be removed from a cell without causing death if the water is removed directly from the frozen state-that is, by sublimation. In support of this concept, drying from the frozen state has been successful in many cases (Flosdorf, 1949) in which dehydration from the liquid state has not. On the other hand, a considerable number of instances have been reported in which freezedrying killed most or all of the organisms. For example, Atkin et al. (1949) reported that 99.98 per cent of brewer's yeast cells fail to survive desiccation; Elser et al. (1935) were, except in rare cases, unable to obtain viable protozoans following freeze-drying; Glover (1946) reported that the technique is exceedingly harmful to Mycobacterium tuberculosis; Raper and Alexander (1945) have found that spores of the Entomophthorales do not survive lyophilization. Until recently freeze-drying has been an empirical technique, and attempts to improve and extend its applications to living cells have been empirical as well. The authors felt, therefore, that studies on the fundamental factors involved in surviving dehydration would be of both theoretical and practical interest. Since intracellular water is apparently a requisite for cell life, an understanding of the factors which determine