224 Atmospheric Life Germs. [April, 



VI. ATMOSPHERIC LIFE GERMS. 

 iT?^)ORD Bacon in the "Novum Organum " (Book II. 



^ \\& Aphorism 13), says, " All putrefaction exhibits some 

 slight degree of heat, though not enough to be per- 

 ceptible to the touch : for neither the substances which by 

 putrefaction are converted into animalculae, as flesh and 

 cheese, nor rotten wood which shines in the dark, are warm 

 to the touch." He thus gives as a definition of spontaneous 

 generation the conversion of substances, such as flesh and 

 cheese, into animalculae. The joke of Dr. Johnson on Tom 

 Davies, a bankrupt bookseller, who took to authorship, that 

 he was " an author generated by the corruption of a book- 

 seller," is evidently a hint as to his connection with Grub 

 Street through an illusion to the popular belief. 



The first recorded facts undermining the old belief in 

 "spontaneous generation," were those of Redi, published 

 in 1638, leading to the first exact experiments in closed 

 vessels of Needham in 1745, and of Spallanzani in 1765 ; 

 the experiments with air purified by heating of Schwann, 

 and with air passed through oil of vitriol of Schultze in 

 1837 ; the proof that the solid particles of yeast alone can 

 cause fermentation by Helmholtz in 1844 ; Schrceder and 

 Dusch's experiments with air filtered through cotton-wool 

 in 1854; and the repetition of the foregoing and complete 

 investigation of the subject by Pasteur in 1802. The object 

 of this paper is to make these last experiments more widely 

 known ; unfortunately they must be stripped of detail, and 

 thereby robbed of much of their strength of argument. 

 Few persons are familiar with the mode of experimenting, 

 the facts observed, and the remarkable chain of evidence 

 afforded by these most carefully-executed, most complete, 

 and therefore most .trustworthy, experiments. 



Pasteur's Microscopic Examination of the Solid Particles 

 Diffused in the Atmosphere. 



The question which Pasteur first set himself to answer 

 was, Is it possible to gain an approximate idea of the re- 

 lation a volume of ordinary air bears to the number of 

 germs that the air may contain ? Let us see what means 

 were taken to determine the number and the nature of 

 floating particles diffused in the air. 



By means of a water aspirator air was drawn from a 

 quiet street, and also from the gardens of the Ecole 

 Normale, in Paris, at some distance from the ground, through 



