THE GENERAL CONDITIONS OF LIFE 299 



seized upon them and claimed that they as the lowest organisms 

 are continually arising at the present time from lifeless matter. 

 But modern bacteriology, with its admirable and delicate methods, 

 for which it is indebted to its founders, especially Pasteur and 

 Robert Koch, has refuted this doctrine again. It has shown that by 

 the exclusion of all germs that can come to the preparation 

 from the outside, even the richest nutrient medium, containing 

 all the substances required for the nutrition of bacteria in the 

 most favourable mixture, remains free from micro-organisms ; and, 

 on the other hand, that a whole world of diverse forms develop in the 

 medium as soon as it is left standing, for a brief time, open to 

 the air. 



Along with this continual strife over the doctrine of spon- 

 taneous generation, attempts have been made, even down to 

 very recent times, to manufacture living organisms artificially 

 in the laboratory. The latest of these attempts is associated 

 especially with the name of Pouchet, who was the last active 

 adherent of the view that it is possible to produce artificially from 

 lifeless matter unicellular organisms, such as bacteria, yeast, and 

 similar microbes, simply by mixing the necessary constituents and 

 putting them under favourable external conditions. Even when 

 at times these experiments have seemed to lead to positive results, 

 the bacteriologists have always appeared with their critical methods, 

 and have shown that in every case there was a development 

 of germs that had come in from the outside or were already 

 present in the vessels used for the experiment. These attempts 

 are really not different from the undertaking of the famulus 

 Wagner to compound man himself from chemical mixtures in a 

 retort. How can one hope to produce chemically even the 

 simplest organism when the chemical composition of living 

 proteids, the most important substances of which all living sub- 

 stance consists, is at present completely unknown ? 



To Haeckel ('66) belongs the credit of having removed from 

 the early absurd ideas of spontaneous generation their sound 

 kernel and of having transferred it to a purely scientific soil. 

 For him the question is indifferent, whether at the present day 

 living substance arises anywhere spontaneously or not. To-day, 

 more than thirty years after Haeckel wrote, and after our know- 

 ledge of the lowest organisms and their reproduction has made so 

 enormous a development, the great majority of investigators are 

 inclined to answer this question negatively. Nevertheless, 

 Haeckel was the first to draw sharply the conclusion that because 

 there was a time when the earth was in a condition that excluded 

 all organic life, living substance must have originated at some 

 time in the earth's development from lifeless substances. Accord- 

 ing to him this time cannot be dated earlier than when the water- 

 vapour, suspended throughout the atmosphere, had been precipi- 



