288 GENERAL PHYSIOLOGY 



they show themselves to be unusually greedy for oxygen. 

 Since it cannot be supposed that without oxygen they are capable 

 of increasing so remarkably as they do in the intestine, and since 

 their greed for free oxygen is acknowledged, it must be assumed 

 that they as well as other Anaerobia, such as the bacteria of 

 tetanus and the bacilli of symptomatic anthrax, are capable in the 

 absence of free oxygen of withdrawing oxygen from the salts of 

 the alkalies that occur in their media in other words, they are 

 able to take oxygen from fixed chemical compounds. This 

 assumption requires experimental proof, and the same may be 

 said also of the other anaerobic parasites of the intestine, 

 which, as, e.g., the thread-worms, according to Bunge's researches 

 ('83), are capable of living in active movement for 4 5 days 

 in a medium completely free from oxygen. 



Finally, organisms in the condition of latent life occupy an 

 exceptional position in respect to oxygen, as to all other vital 

 conditions that bear directly upon metabolism. They require no 

 oxygen, just as they require no food and no water and yet are 

 capable of life. The fact is not unaccountable, for where metabolism 

 cannot be demonstrated, no oxidation-processes are found. 



4. Temperature 



Besides the conditions characterised by the introduction of 

 matter (food, water and oxygen), upon which metabolism directly 

 depends, certain dynamic requirements must be fulfilled, if life is 

 to be maintained. Among them, before all others, is a temperature 

 within certain limits. 



It is well known that chemical compounds are influenced in a 

 marked degree by temperature. In general, high temperatures 

 lead to the dissociation of compounds that at low temperatures 

 can readily exist unchanged. Living substance is a mixture of 

 numerous chemical substances, among which occur highly complex 

 compounds in an extremely labile condition. It is evident, 

 therefore, that living substance also must be dependent in a marked 

 degree upon temperature, that life can exist only within definite 

 temperature-limits. These limits, the minimum and maxi- 

 mum of temperature, are of course very different for different 

 forms of living substance. Temperatures in which some organisms 

 thrive are fatal for others. It is not necessary here to determine 

 for individual species the higher and the lower limits, but it is 

 important to find out what are the minimum and the maximum 

 at which life in general can exist upon the earth's surface. 



The observation has frequently been made that poikilothermal 

 animals and plants can be frozen without losing their vital capacity. 

 Thus, in his polar expedition in the year 1820 John Franklin saw 



