THE LABOURS OF SCHRODER AND DUSCH. 7 



through cotton-wool, the two investigators named above modified, 

 in 1853, the arrangement of Schultze's experiment, by allowing 

 the incoming air to pass through a glass tube packed with cotton- 

 wool before entering the flask. It was found that by means of 

 this (decidedly not "violent") treatment the air also lost its 

 power of causing decomposition and the formation of minute 

 organisms in extracts which would remain unchanged when air 

 was excluded. 



The importance of this demonstration must not, however, be 

 over-estimated, for it only proves the presence in the air of a 

 " something " capable of giving rise to living creatures in inanimate 

 nutrient media, and of exciting substantive changes (fermentation 

 and putrefaction) therein. Concerning the nature of this active 

 " something," the experimenters could give no satisfactory account ; 

 they even left it an open question whether the something was 

 gaseous or not. It may be considered that they were unduly 

 diffident, since the action of the cotton-wool filter proves that 

 this something must necessarily be a solid body and not a gas. 

 But on the other hand, both investigators could point to experi- 

 ments wherein the previously boiled test liquid afterwards under- 

 went decomposition, notwithstanding the fact that all the air 

 which was allowed access to it had been filtered through cotton- 

 wool. Milk they had, in their first treatise, recognised as such a 

 liquid, and to this were added, in a second communication by 

 SCHRODER (I.), yolk of egg, meat, and meat broth, in all of which 

 cases the filtration of the air proved useless. This led Schroder 

 to separate the phenomena of decomposition characterised as 

 fermentation and putrefaction into two groups : the one, which 

 he designated "voluntary decomposition," requiring only oxygen 

 for its inception, whilst the other, e.g. the fermentation of wort, 

 required, in addition, the collaboration of that unknown constituent 

 of the air, which could be destroyed by fire or arrested by a cotton- 

 wool filter. " Whether this active substance should be regarded 

 as germs floating in the air, or as some hitherto unknown chemical 

 substance modified by high temperature and separated and fixed 

 by the influence of contact with the cotton fibres, must remain 

 undecided." 



Glancing back for a moment at the work of Schultze, one would 

 be only too readily disposed to consider the results of Schroder 

 and Dusch's experiment as a retrograde step, since they not only 

 did not afford us any further information beyond that established 

 by Schultze as to the nature of the germs in the air, but also 

 called in question the accuracy of Schultze's results. And, in fact, 

 repetitions of the Schultze experiment by many other workers, with 

 various modifications, especially with regard to the kind of test 

 liquid employed, confirmed the results of Schroder and Dusch. 

 In numerous instances decomposition ensued, even in the boiled 

 liquid, when purified air (filtered or heated to redness) alone was 



