METHODOLOGICAL INTRODUCTION. 9 



attainable in the case of mineral analyses. Animal chemistry is 

 still wholly unable to afford us a precise, and at the same time a 

 practically useful method of investigating the blood; and how 

 should it be otherwise while we continue to be in doubt regarding 

 the chemical nature of its ordinary constituents ? The mineral 

 substances of normal blood are not yet determined, or, at all 

 events, continue to be made the subject of dispute ; we scarcely 

 know the names of the fatty matters it contains ; one of its most 

 important constituents, fibrin, cannot be chemically exhibited in 

 a pure state ; we are ignorant of the nature and mode of secretion 

 of the globulin of the blood-corpuscles ; we are still far from being 

 able to separate arid determine the so-called protein oxides ; and 

 we are also ignorant of the excrementitious substances occurring 

 in the blood. How then, amidst these and a thousand other 

 uncertainties and doubts, can an investigation of the blood be 

 scientifically and trustworthily conducted ? We analyse healthy 

 and morbid milk, and yet we are ignorant of the substances whose 

 admixture we have termed casein. The urine, in its morbid con- 

 dition, presents many varieties; and yet our knowledge of this 

 secretion, frequently as it has been analysed, amounts to little more 

 than an acquaintance with the quantitative relations of some of 

 its principal constituents ; creatinine and hippuric acid have not 

 been determined by any analysis, and doubts are still enter- 

 tained by some chemists, (although most unjustly,) regarding the 

 presence of the latter in human urine, while absolutely nothing 

 is known regarding the most important pigment of this secre- 

 tion. Many experiments have been made and theories broached 

 on nutrition and digestion, and yet to almost the present day 

 the existence of lactic acid in the gastric juice has been con- 

 tested. Although hypotheses are not wanting regarding the mode 

 of action of pepsin, we know nothing of its* chemical nature, 

 and we are wholly ignorant of the proximate metamorphosis 

 of albuminous bodies in the stomach during the process of 

 digestion. Will Mulder be able, even with his most accu- 

 rate analyses, to support his protein th3ory by the aid of sul- 

 phamule and phosphamide? or is this term destined merely to 

 indicate a past epoch of organic chemistry ? When such is the 

 state of animal chemistry, can we wonder that there should be 

 obscurity regarding the chemical processes in the animal body, 

 their various isolated and combined actions, their causal connexion 

 and their dependence on external influences and internal con- 

 ditions ? Unfortunately, we might be led to believe, from the 



