THE PROCESS OF OXIDATION. 235 



stomachs of rabbits and dogs (concentrated solutions must 

 necessarily be avoided, as they always induce a morbid condition 

 in the animals), the result to be expected would naturally be, that 

 when the animals had been fed on oats only, or on some food equally 

 poor in alkalies, the normal alkalinity of the blood would be so 

 much diminished that the sugar which had now been conveyed 

 to the blood from the intestine or the liver would not be perfectly 

 oxidised, and would therefore pass into the urine in an undecom- 

 posed state. This conjecture has not, however, been verified by 

 my experiments. The urine does not even exhibit any trace of 

 sugar when attempts are made to remove the alkali from the blood 

 by artificial means. Similar but variously modified experiments 

 have also been made by Uhle,* with precisely similar results. It 

 would, of course, be an utterly useless experiment to attempt to 

 gain the same object by injecting acids into the blood. 



We must not, however, form too high an opinion of the oxidis- 

 ing force of the blood, however important it may be to the entire 

 animal economy. Thus, for example, we meet with numerous 

 phenomena which indicate the co-existence of a deoxidising pro- 

 cess with the process of oxidation ; of these we need only instance 

 the formation of substances so rich in sulphur as taurine and 

 cystine, and of others so poor in oxygen as cholesterin, castorin, &c. 

 The most striking illustration of this fact is afforded by the well- 

 known experiment, which has recently been confirmed by one of 

 my pupils, Ranke,f that the animal organism acts upon indigo in 

 the same reducing manner as the hot or cold vat ; ordinary indigo 

 blue is converted in the primse viae into sub-oxide of isatin, (re- 

 duced indigo), and may, when dissolved in an alkaline solution, 

 pass through the blood without being perfectly oxidised ; hence 

 it may re-appear in an unoxidised state in the urine. If we observe 

 the urine that is discharged after the administration of a few 

 grammes of indigo, we perceive that the fluid assumes a light blue 

 colour, which becomes gradually more intense if it is shaken for a 

 time in the air, until a blue sediment of pure indigo blue is finally 

 formed. This reduction does not originate in the urine itself, since 

 the alkaline fermentation must be set up in the fluid before it can 

 dissolve indigo. This urine, however, has always an acid reaction. 

 If we had not the most evident proof before us that free oxygen was 

 contained in the blood, an unphysiological chemist might consider 

 himself justified in concluding from these facts, that oxygen can- 



* Diss. inaug. med. Lips. 1852, p. 19. 

 f Journ. f. pr. Chem. Bd. 56, S. 17. 



