ITS INCIDENTAL CONSTITUENTS. 421 



matters pass unchanged, or only slightly modified, into the urine ; 

 as, for instance, the colouring matters of indigo, madder, gamboge, 

 rhubarb, logwood, red beet, and whortleberries, and the odorous 

 constituents of valerian, garlic, asafcetida, castoreum, saffron, and 

 turpentine. Wohler could not rediscover the following substances 

 in the urine : Camphor, resins, empyreumatic oil, musk, alcohol, 

 ether, cochineal, litmus, sap-green, or alcanna. 



Another point worthy of notice is the rapidity with which many 

 substances pass through the animal organism. We may generally 

 assume that the rapidity with which a substance re-appears in the 

 urine is directly proportional to its solubility, and inversely pro- 

 portional to the amount of change which it undergoes in the animal 

 organism. This rule, however, has many exceptions, amongst 

 which we may especially mention iodide of potassium a substance 

 which is so easy of detection, even in extremely minute quantities ; 

 according to some observers it may be detected in the urine in from 

 four to ten minutes after it has entered the mouth. I have only 

 been able to observe this in a man in whom the posterior wall of 

 the bladder, with the openings of the ureters, lay exposed ; in othei 

 persons it often did not appear in the urine till after a period 

 varying from three quarters of an hour to five hours, while, on the 

 other hand, it was very soon to be detected in the saliva (see p. 23). 

 After the ingestion of from two to three drachms of bicarbonate of 

 potash, I have found, in experiments on several persons, that the 

 urine became neutral in from thirty to forty-five minutes, and 

 alkaline in the course of an hour. Lactate of soda taken to the 

 extent of half an ounce, rendered normal urine alkaline in half an 

 hour ; on injecting similar quantities of the same salt into the jugular 

 veins of dogs, their urine became strongly alkaline after five, or at 

 the longest after twelve, minutes. 



There is great diuresis in dogs after this operation if we provide 

 them with plenty to drink ; the loss of blood, even when small, 

 seems to excite their thirst, while, on the other hand, the alkaline 

 carbonate that is formed probably actually hastens the secretion of 

 urine. Hence it is in general very easy to observe the time at 

 which such urine becomes alkaline. 



Erichson* observed the period of the transmission of soluble and 

 colouring substances into the urine in a man with extroversion of the 

 bladder probably the same person who had been travelling about 

 Germany; after administering forty grains of ferrocyanide of 

 potassium, he saw it re-appear within two minutes in the unn 

 * Lond. Med, Gaz. June, 1845, 



