2 ANIMAL JUICES. 



the experimentalist should be familiar with certain anatomico- 

 surgical operations, we think it will hardly be deemed superfluous, 

 if we consider the methods adopted for procuring some of the 

 animal juices. 



When we have obtained a physiologically pure substance, 

 studied its physical characters, and determined by the microscope 

 the presence or absence of morphological elements, we must next 

 consider the method in which the chemical analysis should be 

 conducted. It is obvious that the plan and method of the analysis 

 may vary in accordance with the special aims of the investiga- 

 tion, and will in general depend upon the nature of the con- 

 stituents of the fluid. We have therefore thought it expedient 

 to indicate the analytical methods of analysis suited to the different 

 fluids. But as we are still on the very threshold of the enquiry, 

 we can do no more than present the rudiments of a future organic 

 analytical chemistry. As we have already observed in the first 

 volume, physiological chemistry, considered as an inductive science, 

 requires most especially to be based on exact principles amenable 

 to calculation. Unfortunately, however, all chemists concur in 

 admitting that a large number of analyses of the animal fluids rank 

 among the most slovenly and unprincipled investigations of their 

 science. How many of these show at the first glance that they 

 are utterly worthless ! In such a state of things it will scarcely be 

 deemed superfluous to specify some few of the properties which it 

 is necessary for the analysis to possess in order to render it of any 

 value in a scientific point of view. 



As we have already referred in the first volume to the qualitative 

 and quantitative determinations of the individual animal substrata, 

 it only remains for us to observe, in reference to compound fluids 

 generally, that in the qualitative analysis of the animal juices, 

 the largest possible quantity should be employed a point the 

 importance of which was first fully demonstrated by Liebig^s 

 investigations regarding the juices of the flesh, &c. For quantitative 

 zoo-chemical analyses, however, the converse rule holds good, more 

 especially in analyses of the blood. We generally find that too 

 large a quantity has been employed for the determination of the 

 individual constituents in the majority of the blood-analyses on 

 record. As a general rule, it may be asserted that quantitative 

 analyses of the blood and of similar fluids, are the less exact in 

 proportion to the quantity of the substance analysed. This 

 depends partly on the difficulty frequently experienced in passing 

 animal fluids, even when diluted, through a filter, partly on the 



