POISONS, CONTAGIONS, MIASMS. 



liJ 



wnich exercises a medicinal influence when 

 nitrate of silver is administered ; the remain- 

 ing chloride of silver is eliminated from the 

 body in the ordinary way. Solubility is 

 necessary to give efficacy to any substance 

 in the human body. 



The soluble salts of lead possess many 

 properties in common with the salts of silver 

 and mercury ; but all compounds of lead 

 with organic matters are capable of decom- 

 position by dilute sulphuric acid. The dis- 

 ease called painter's colic is unknown in aL 

 manufactories of white lead in which the 

 workmen are accustomed to take as a pre- 

 servative sulphuric acid lemonade (a solu- 

 tion of sugar rendered acid by sulphuric 

 acid.) 



The organic substances which have com- 

 bined in the living body with metallic oxides 

 or metallic salts, lose their property of im- 

 bibing water and retaining it, without at the 

 same time being rendered incapable of per- 

 mitting liquids to penetrate through their 

 pores. A strong contraction and shrinking 

 of the surface is the general effect of contact 

 with these metallic bodies. But corrosive 

 sublimate, and several of the salts of lead, 

 possess a peculiar property, in addition to 

 those already mentioned. When they are 

 present in excess, they dissolve the first 

 formed insoluble compounds, and thus pro- 

 duce an effect quite the reverse of contrac- 

 tion, namely, a softening of the part of the 

 body on which they have acted. 



Salts of oxide of copper, even when in 

 combination with the most powerful acids, 

 are reduced by many vegetable substances, 

 particularly such as sugar and honey, either 

 into metallic copper, or into the red sub- 

 oxide, neither of which enters into combina- 

 tion with animal matter. It is well known 

 that sugar has been long employed as the 

 most convenient antidote for poisoning by 

 copper. 



With respect to some other poisons, 

 namely, hyclrocyanic acid and the organic 

 bases strychnia and brucia, we are ac- 

 quainted with no facts calculated to eluci- 

 date the nature of their action. It may, 

 however, be presumed with much certainty, 

 that experiments upon their mode of action 

 on differen* animal substances would very 

 quickly lead to the most satisfactory conclu- 

 sions regarding the cause of their poisonous 

 effects. 



There is a peculiar class of substances, 

 which are generated during certain pro- 

 cesses of decomposition, and which act upon 

 the animal economy as deadly poisons, not 

 on account of their power of entering into 

 combination with it, or by reason of their 

 eontairiing a poisonous material, but solely 

 by virtue of their peculiar condition. 



In order to attain to a clear conception of 

 the mode of action of these bodies, it is ne- 

 cessary to call to mind the cause on which 

 we have shown the phenomena of fermen- 

 tation, decay, and putrefaction to depend. 



This cause may be expressed by the fol- 



lowing law, long since proposed by La Plare 

 and Berthollet, although its truth with re- 

 spect to chemical phenomena has only lately 

 been proved. "*# molecule set in motion by 

 any power can impart its own motion to 

 another molecule with which it may be in 

 contact." 



This is a law of dynamics, the operation 

 of which is manifest in all cases, in wh.ch 

 the resistance (/brce, affinity, or cohesion,) 

 opposed to the motion is not sufficient to 

 overcome it. 



We have seen that ferment or yeast is a 

 body in the state of decomposition, the 

 atoms of which, consequently, are in a state 

 of motion or transposition. Yeast placed 

 in contact with sugar communicates to the 

 elements of that compound the same state, 

 in consequence of which, the constituents 

 of the sugar arrange themselves into new 

 and simpler forms, namely, into alcohol and 

 carbonic acid. In these new compounds 

 the elements are united together by stronger 

 affinities than they were in the sugar, and 

 therefore under the conditions in which 

 they were produced further decomposition 

 is arrested. 



We know, also, that the elements of 

 sugar assume totally different arrangements, 

 when the substances which excite their 

 transposition are in a different state of de- 

 composition from the yeast just mentioned. 

 Thus, when sugar is acted on by rennet or 

 putrefying vegetable juices, it is not con- 

 verted into alcohol and carbonic acid, but 

 into lactic acid, mannite, and gum. 



Again, it has been shown, that yeast 

 added to a solution of pure sugar gradually 

 disappears, but that when added to vege- 

 table juices which contain gluten as well as 

 sugar, it is reproduced by the decomposition 

 of the former substance. 



The yeast with which these liquids are 

 made to ferment has itself been originally 

 produced from gluten. 



The conversion of gluten into yeast in 

 these vegetable juices is dependent on the 

 decomposition (fermentation) of sugar; for, 

 when the sugar has completely disappeared, 

 any gluten which may still remain in the 

 liquid does not suffer change from contact 

 j with the newly-deposited yeast, but retains 

 all the characters of gluten. 



Yeast is a product of the decomposition 

 of gluten ; but it passes into a second stage 

 of decomposition when in contact with 

 water. On account of its being in this 

 state of further change, yeast excites fermen- 

 jtation in a fresh solution of sugar, and if 

 this second saccharine fluid should contain 

 gluten, (should it be wort, for example,) 

 yeast is again generated in consequence of 

 the transposition of the elements of the 

 sugar exciting a similar change in this 

 gluten. 



After this explanation, the idea that yeast 

 reproduces itself as seeds reproduce seeds, 

 cannot for a moment be entertained. 



From the foregoing facts it follows, tnat 



