240 PRINCIPLES OF GENERAL PHYSIOLOGY 



so that it must be hastened by a catalyst. Hence the universal presence of 

 enzymes in the organism. 



Although water, as such, is chemically so inert a substance, certain chemical individuals, 

 such as sodium, enter into violent reaction with it. Here again, however, we are met with 

 the possibility that the reaction is accelerated, or even rendered possible, onl}' by the presence 

 ol some other substance, which acts as a catalyst. H. Brereton Baker (1910) and Baker and 

 Parker (1913) have shown how greatly the rate of reaction between sodium amalgam and 

 water is retarded by purification of the water. 



DRYING AND STERILISATION 



The necessity of the presence of water for the manifestation of vital properties 

 is sufficiently obvious from the former part of this chapter. An interesting 

 question arises as to how far protoplasm can be deprived of water, while remaining 

 capable of recovery to life, when again supplied with moisture. 



That drying in ordinary air is not necessarily fatal is shown by every-day 

 experience with seeds, which can be kept a large number of years without losing 

 their power of germination. 



Shattock and Dudgeon (1912) have shown, moreover, that certain bacteria, 

 even when they do not produce spores, can be exposed to a vacuum, produced 

 by charcoal surrounded by liquid air, for a space of one hundred and sixteen 

 days. One would suppose that all water would be removed from the organisms 

 in this way. Mr Shattock informs me, that he has found, since the paper 

 referred to was published, that after two years in the vacuum, Bacillus pyocyaneus 

 was still capable of vigorous growth. 



Apparently, under such conditions, all chemical processes cease, so that we 

 must assume that the protoplasm remains in the state in which it was at the 

 moment of desiccation and prepared to resume activity on the arrival of water. 

 It is interesting to note that the bacillus in question lives longer in the dry vacuum 

 than when merely air dried ; in this latter state it never survived longer than nine 

 days, no doubt owing to chemical changes still continuing. Some kind of change 

 can be brought about, even in the perfectly dry condition, since, if exposed to 

 sunlight or ultra-violet radiation, it was found by Shattock and Dudgeon that 

 bacteria were killed rapidly, even in the absolutely dry vacuum. 



Naturally, the much more complex and sensitive organisation of the higher 

 animals cannot be dried in this way. It is well known, however, that creatures 

 as highly developed as Rotifers survive drying in air ; but this appears to be 

 due to the production of a capsule which prevents complete loss of water. Davis 

 (1873) saw a drop of fluid exude when he punctured the cyst of Philodina. 



It seems possible that desiccation at the eutectic temperature bj- Altmann's method, 

 described in the first chapter of this book (page 17), might allow of recover}- of the cells of 

 higher organisms. If so, a valuable means of investigation would be available: tissue. 

 dehydrated in this way, can be cut into thin sections and the cells observed under tin- 

 microscope. The difficulty, as previously mentioned, comes in when it is required to add 

 water again. 



An important practical application of the facts described above, as to the 

 necessity of the presence of water for protoplasmic activity, lies in the greater 

 resistance of organisms to the action of heat the drier they are. This is, however, 

 not invariably the case Bacillus pyocyaneus is killed by exposure to 65 for 

 an hour, wet or dry. The resistance is particularly noticeable in the case of 

 spores of bacteria and other fungi ; as is well known, a higher temperature of 

 sterilisation is required to kill them. This behaviour is also shown by enzymes, 

 which resist a considerably higher temperature in the dry state than when 

 in solution. 



A fact worth recording here is that, as shown by Dreyer and Ainley Walker 

 (1912), spores of bacteria suspended in glycerol or oil are not killed by exposure 

 to a temperature of 119 C. for over half an hour. This fact is obviously of 

 much practical importance, since sterilisation in non-watery liquids is frequently 

 made use of. 



That organisms are under more or less risk of injury from drying is shown by 

 the precaution taken by many of them to avoid the risk by surrounding them- 



