568 Microscopic Organisms in Blood and their Relation to Disease, [part hi. 



refer briefly to the more salient circumstances which have conduced to make the 

 present doctrine of the causative relation to disease of these low forms of plant- 

 life so attractive to botanists and to the medical profession. " The foundations of 

 the germ theory of disease in its most commonly accepted form," writes Dr. 

 Charlton Bastian,* " were laid in 1836 and shortly afterwards. The discovery at this 

 time of the yeast-plant by Schwann and Cagniard-Latour soon led to the more 

 general recognition of the almost constant association of certain low organisms with 

 different kinds of fermentations. But it was not till twenty years afterwards that 

 Pasteur announced, as the result of his apparently conclusive researches, that low 

 organisms acted as the invariable causes of fermentations and putrefactions ; that such 

 changes, in fact, though chemical processes, were only capable of being initiated by 

 the agency of living units." These observations and the interpretations applied to 

 them very rapidly caught the ear of the medical profession, as from a very early 

 period in the history of medicine the supposition that disease was propagated by 

 means of a ferment — a leaven — had taken a firm hold. Previous to the publication of 

 M. Pasteur's observations, a physico-chemical theory had been almost universally 

 acknowledged as sufficiently explanatory of the phenomena manifested by certain classes 

 of disease. This was notably the case with regard to the fermentation-doctrine of 

 Liebig, a doctrine the truth of which he strongly advocated until the day of his death 

 in 1873, and which, somewhat modified as a result of later researches, is still upheld 

 by some of the most eminent chemists of our own time. 



The leading features of the " vital " and the " physico-chemical " theories of 

 fermentation I have recently been lucidly summarised by Mr. C. T. Kingzett in a 

 paper read before the Society of Arts. % With regard to the first of these views 

 and in illustration of them this chemist remarks : " When a solution of sugar is 

 exposed to the action of the healthy yeast it suffers a change ; the atoms comprised 

 in its molecules are broken up and re-arranged into new forms which are recognised 

 as alcohol and carbonic dioxide. Glycerine and succinic acid are also formed at the 

 expense of the sugar, but the lactic acid which generally accompanies alcoholic 

 -fermentation is considered as proved to be due to the presence of a ferment distinct 

 from, but accompanying, the yeast. . . . The fermentation alluded to is regarded 

 as a particular instance of a biological re-action, manifesting itself as the result of a 



* Paper read before the Pathological Society of London, April 6th, 1875. Lancet, vol. i, page 501, 1875. 

 Brithli Medical Jmirnal, vol. i, page 469, 1875. 



f " Certain organic compounds, when exposed to the action of the air, water, and a certain temperature, 

 undergo decomposition, consisting either in a slow combustion or oxidation by the surrounding air, or in a new 

 arrangement of the elements of the compound in different proportions (often with assimilation of the elements of 

 water), and the consequent formation of new products. The former process, that of slow combustion, is called 

 Eremai'atiHls or Decay ; the latter is called Putrefartwn or Fermentation— jnttref action, when it is accompanied 

 by an offensive odour, fermentation, when no such odour is evolved, and especially if the process results in the 

 formation of useful products ; thus, the decomposition of a dead body, or of a quantity of blood or urine, is putre- 

 faction : that of grape-juice or malt-wort, which yields alcohol, is fermentation." — WatVs Dictionary of 

 C7),emi-«try, vol. ii, p. 624. 1872. 



J Jmrnal of the Society of Arti, March 1878. 



