370 POISONS, CONTAGIONS, MIASMS. 



ble in water, and without the slightest taste), be brought into 

 contact with another comjKnmd B, which is to be reproduced ; 

 and if this second body be oxalic acid dissolved in water, then 

 the following changes are observed to take place : — the oxamide 

 is decomposed by the oxalic acid, provided the conditions neces- 

 sary for their exercising an action upon one another are present. 

 The elements of water unite with the constituents of oxamide, 

 and ammonia is one product formed, and oxalic acid the other, 

 both in exactly the proper proportions to combine and form a 

 neutral salt. 



Here the contact of oxamide and oxalic acid induces a trans- 

 formation of the oxamide, which is decomposed into oxalic acid 

 and ammonia. The oxalic acid thus formed, as well as that 

 originally added, are neutralized by the ammonia — as far as that 

 product suffices to neutralize them ; but, of course, as much free 

 oxalic acid exists after the decomposition as before it, and is still 

 possessed of its original power. It matters not whether the free 

 oxalic acid is that originally added, or that newly produced ; it 

 is certain that it has been reproduced in an equal quantity by 

 the decomposition. 



If we now add to the same mixture a fresh portion of oxamide, 

 exactly equal in quantity to that first used, and treat it in the 

 same manner, the same decomposition is repeated ; the free oxalic 

 acid enters into combination whilst another portion is liberated. 

 In this manner a very minute quantity of oxalic acid may be 

 made to effect the decomposition of several hundred pounds of 

 oxamide ; and one grain of the acid to reproduce itself in un- 

 limited quantity. 



We know that the contact of the virus of small-pox causes 

 such a change in the blood, as gives rise to the reproduction of 

 the poison from the constituents of the fluid. This transforma- 

 tion is not arrested until all the particles of the blood susceptible 

 of the decomposition have undergone the metamorphosis. We 

 have just seen that the contact of oxalic acid with oxamide caused 

 the production of fresh oxalic acid, which in its turn exercised 

 the same action on a new portion of oxamide. The transforma- 

 tion was only arrested in consequence of the quantity of oxamide 

 present bein r limited. In their form both these transformations 



