534 Chemical Physiology and Pathology. 



by Laplace and Berthollet. " An atom set in motion by any 

 power can communicate its motion to another atom, which 

 is in contact with it." The blood has no power in itself to 

 produce metamorphoses ; its chief characteristic is its being 

 ready to undergo them. Decaying and diseased substances 

 work in it, as yeast in a fermenting mixture. Thus, poison- 

 ous sausages impart their state of decomposition to the living 

 organism, and the patient dries up to the condition of a 

 mummy. Poisons of this sort are produced in the living body 

 also, as in measles, the plague, syphilis, &c. These conta- 

 gions may retain their power for a long time without being 

 destroyed, if their peculiar state of decomposition be pre- 

 served, (as by dry weather). Some have attributed to con- 

 tagion a peculiar (parasitic) life, as if it were the germ of a 

 seed ; some have sought for its causes in the presence of 

 microscopic forms, but Liebig explains its operation by its 



peculiar state of decomposition. A miasma works by 



its chemical character, in as much as it forms combina- 

 tions, or causes decompositions : it excites disease, without 

 reproducing itself : it does not by its peculiar nature cause a 

 gradual decomposition like contagion, but works directly as 

 a poison. 



Oxides of proteine. All the constituents of compounds 

 containing nitrogen, are formed from proteine : the most 

 important are the phosphorus and sulphur compounds of pro- 

 teine (albumen, fibrine, caseine). Every atom of proteine, 

 which has once served in the production of a vital pheno- 

 menon, is to be considered as dead, and the most easily 

 eliminated form, in which in men and in the carnivora the 

 dead proteine is excreted from the body, is that of urea. Its 

 formation is therefore unceasing, and its excretion from the 

 body constant and uninterrupted. Only oxygen and water 

 take part in its formation, and thus urea is an oxide or oxy- 



hydrate of proteine. If now we carry with us the idea, 



that. the oxygen (and water) unites with the compounds of 



. 



