316 Dr. F. W. Pavy on the Physiology of [June 14, 



indicated how much sugar each c. c. of this liquid contains, the data are 

 afforded for ascertaining the quantity of sugar in the volume corre- 

 sponding with the weight of blood analyzed, and thence the ratio per 

 1000. 



There are two seriously faulty points about the method as a quan- 

 titative process of analysis. 



The first is the assumption that the volume of the trial liquid cor- 

 responds in c. c. with -f of the weight in grms. of the mixture of sul- 

 phate of soda and blood. In reality, the actual relation between the 

 volume of liquid obtained and the weight of the mixture employed must 

 vary in each individual instance with the proportion of solid matter 

 existing in the particular specimen of blood, and the loss of liquid by 

 evaporation from the capsule during the process of coagulation by heat.. 

 It may be regarded as totally impossible to secure that the coagula- 

 tion of the albuminous and colouring matters can be effected, in an 

 open capsule at the high temperature necessary, with identically the 

 same loss by evaporation in each individual instance ; and as the amount 

 of liquid derivable from the mixture is not large, a slight variation 

 must alter to a decided extent the result, especially when it is worked 

 out into the proportion in 1000 parts. With 20 grms. of blood as the 

 quantity submitted to analysis, any error existing in the result yielded 

 becomes multiplied 50 times when the representation of ratio per 1000 

 is made. 



The other point is, that the process involves the influence of organic 

 matter in preventing the deposition of the suboxide of copper. It is 

 not the usual principle of applying the test that is appealed to. In the 

 ordinary volumetric process of analysis with the copper solution, atten- 

 tion is given to the separation of suboxide till the whole of the copper 

 has been removed from the liquid. In Bernard's process a large addi- 

 tion of potash is employed (20 to 25 c. c. of a concentrated solution to 

 1 c. c. of the copper test), the effect of which is to act upon some one or 

 other organic principle left in the liquid obtained from the blood, and 

 prevent a deposit of suboxide occurring. The presence of the potash does 

 not by its own action interfere with the fall of suboxide ; for when the 

 process is carried out upon a simple solution of sugar, the suboxide falls 

 in the usual way, whilst in the case of the liquid obtained from the 

 blood, the removal of blue colour takes place without any signs of ap- 

 pearance of precipitate. Without the addition of the potash the usual 

 behaviour occurs. 



Actual observation shows that the results yielded by Bernard's pro- 

 cess are very wide of those given by a process to be presently described, 

 which is founded upon the precipitation of the suboxide and the subse- 

 quent collection of the copper by means of galvanic action upon a 

 cylinder of platinum foil, as is now extensively done in the assaying of 

 copper ores. This application of the copper solution yields a gravimetric 

 instead of a volumetric process of analysis. There is nothing in it of a 



