2 H. O. HALVORSON 



fungi, and algae; viable forms rendered inactive by freezing; the 

 cysts of protoza; and the spores of bacteria. I wish to discuss 

 each of these in some detail under the headings of dehydrated 

 forms, seeds, buds, cysts, insects, and spores. 



DEHYDRATED FORMS 



Keilin refers to this as a state of anhydrobiosis. In this state, 

 forms seem to be lifeless because of lack of water. The inert, dry, 

 yet viable protozoa were first observed by Leeuwenhoek when 

 he showed that gutter-sand and dirt which had been kept in his 

 laboratory for some time in a very dry condition, contained 

 viable protozoa. They could be observed to be living and active 

 immediately after sterile water was added to the material. 

 Similar observations have been made by biologists from that 

 day to the present. It is now well estabhshed, therefore, that 

 many protozoa and some metazoans such as rotifers, tardi- 

 grades, and nematodes, can be dried to the point where there is 

 virtually no moisture left; these can be shown to be viable and 

 unharmed, however, when rehydrated. Not only will they 

 withstand this desiccation, but they can also be stored for long 

 periods of time in the desiccated condition without, seemingly, 

 much loss of viability. Similar experiments have been performed 

 with many forms of fungi and bacteria. I am not familiar with 

 the literature on algae, but it certainly must be true that many of 

 their forms also can be desiccated in like manner and remain 

 viable. This seems to be nature's way of preserving these forms 

 through periods of drought and transport. 



It cannot be presumed, however, that complete desiccation 

 and storage in the dry state does not damage the cells in some 

 manner. This has been shown with bacteria that have been 

 preserved by desiccation or lyophilization^' ^. When one 

 makes quantitative studies of the number of viable cells present 

 before and after drying and rehydration, one can show that 

 many of the individual cells die in the process. Why some cells 

 live and others die is certainly not known. It can be due to a 



