Only the closing years of the century witnessed the rise of the experimental methods in physics and chemistry, owing to the brilliant work of Priestley and of Lavoisier. The foundations of general physiology had been laid by Haller,[109] those of embryology to a partial extent by Wolff,[110] Von Baer's work not appearing until 1829, the year in which Lamarck died. _Spontaneous Generation._--Lamarck's views on spontaneous generation are stated in his _Recherches sur l'Organisation des Corps vivans_ (1802). He begins by referring to his statement in a previous work[111] that life may be suspended for a time and then go on again. "Here I would remark it (life) can be produced (_préparée_) both by an organic act and by nature herself, without any act of this kind, in such a way that certain bodies without possessing life can be prepared to receive it, by an impression _which indicates in these bodies the first traces of organization_." We will not enter upon an exposition of his views on the nature of sexual generation and of fecundation, the character of his _vapeur subtile_ (_aura vitalis_) which he supposes to take an active part in the act of fertilization, because the notion is quite as objectionable as that of the vital force which he rejects. He goes on to say, however, that we cannot penetrate farther into the wonderful mystery of fecundation, but the opinions he expresses lead to the view that "nature herself imitates her procedures in fecundation in another state of things, without having need of the union or of the products of any preëxistent organization." He proceeds to observe that in the places where his _aura vitalis_, or subtle fluid, is very abundant, as in hot climates or in heated periods, and especially in humid places, life seems to originate and to multiply itself everywhere and with a singular rapidity. "In this high temperature the higher animals and mankind develop and mature more rapidly, and diseases run their courses more swiftly; while on the other hand these conditions are more favorable to the simpler forms of life, for the reason that in them the orgasm and irritability are entirely dependent on external influences, and all plants are in the same case, because heat, moisture, and light complete the conditions necessary to their existence. "Because heat is so advantageous to the simplest animals, let us examine whether there is not occasion for believing that it can itself form, with the concourse of favorable circumstances, the first germs of animal life. "_Nature necessarily forms generations, spontaneous or direct, at the extremity of each organic kingdom or where the simplest organic bodies occur._" This proposition, he allows, is so far removed from the view generally held, that it will be for a long time, and perhaps always, regarded as one of the errors of the human mind.